Position-dependent intra-prediction combination for angular intra-prediction modes for video coding

ABSTRACT

An example device for decoding video data includes a memory configured to store video data; and one or more processors implemented in circuitry and configured to: generate an intra-prediction block for a current block of video data using an angular intra-prediction mode, the angular intra-prediction mode being an upper-right angular intra-prediction mode or a lower-left angular intra-prediction mode; determine a prediction direction of the angular intra-prediction mode; for at least one sample of the intra-prediction block for the current block: calculate a gradient term for the at least one sample along the prediction direction; and combine a value of an intra-predicted sample of the intra-prediction block at a position of the at least one sample of the intra-prediction block with the gradient term to produce a value of the at least one sample of the intra-prediction block; and decode the current block using the intra-prediction block.

This application is a continuation of U.S. patent application Ser. No.17/115,455, filed Dec. 8, 2020, which claims the benefit of U.S.Provisional Application No. 62/945,725 filed Dec. 9, 2019, and U.S.Provisional Application No. 62/989,316, filed Mar. 13, 2020, the entirecontents of each of which are incorporated by reference.

TECHNICAL FIELD

This disclosure relates to video coding, including video encoding andvideo decoding.

BACKGROUND

Digital video capabilities can be incorporated into a wide range ofdevices, including digital televisions, digital direct broadcastsystems, wireless broadcast systems, personal digital assistants (PDAs),laptop or desktop computers, tablet computers, e-book readers, digitalcameras, digital recording devices, digital media players, video gamingdevices, video game consoles, cellular or satellite radio telephones,so-called “smart phones,” video teleconferencing devices, videostreaming devices, and the like. Digital video devices implement videocoding techniques, such as those described in the standards defined byMPEG-2, MPEG-4, ITU-T H.263, ITU-T H.264/MPEG-4, Part 10, Advanced VideoCoding (AVC), ITU-T H.265/High Efficiency Video Coding (HEVC), andextensions of such standards. The video devices may transmit, receive,encode, decode, and/or store digital video information more efficientlyby implementing such video coding techniques.

Video coding techniques include spatial (intra-picture) predictionand/or temporal (inter-picture) prediction to reduce or removeredundancy inherent in video sequences. For block-based video coding, avideo slice (e.g., a video picture or a portion of a video picture) maybe partitioned into video blocks, which may also be referred to ascoding tree units (CTUs), coding units (CUs) and/or coding nodes. Videoblocks in an intra-coded (I) slice of a picture are encoded usingspatial prediction with respect to reference samples in neighboringblocks in the same picture. Video blocks in an inter-coded (P or B)slice of a picture may use spatial prediction with respect to referencesamples in neighboring blocks in the same picture or temporal predictionwith respect to reference samples in other reference pictures. Picturesmay be referred to as frames, and reference pictures may be referred toas reference frames.

SUMMARY

In general, this disclosure describes techniques for performingposition-dependent intra-prediction combination (PDPC) for angularintra-prediction modes. In PDPC, a video coder (encoder or decoder)generally predicts samples of a prediction block using samples of aprimary boundary, then uses samples of a secondary (orthogonal) boundaryto modify the predicted samples. For instance, if the primary boundaryis an upper boundary of a current block, the video coder may use samplesof a left boundary of the current block as the secondary boundary.Likewise, if the primary boundary is the left boundary, the video codermay use the upper boundary as the secondary boundary. In some instances,samples of the secondary boundary may not be available, e.g., due to anangle of an intra-prediction direction for the current block.Conventionally, PDPC is disabled in these scenarios. However, accordingto the techniques of this disclosure, the video coder may performgradient PDPC, in which case the video coder may calculate a gradientterm for a sample and use the gradient term to produce a value of the atleast one sample of the intra-prediction block, instead of an actualsample of the secondary boundary.

In one example, a method of decoding video data includes generating anintra-prediction block for a current block of video data using anangular intra-prediction mode, the angular intra-prediction mode beingan upper-right angular intra-prediction mode or a lower-left angularintra-prediction mode; determining a prediction direction of the angularintra-prediction mode; for at least one sample of the intra-predictionblock for the current block: calculating a gradient term for the atleast one sample along the prediction direction; and combining a valueof an intra-predicted sample of the intra-prediction block at a positionof the at least one sample of the intra-prediction block with thegradient term to produce a value of the at least one sample of theintra-prediction block; and decoding the current block using theintra-prediction block.

In another example, a device for decoding video data includes a memoryconfigured to store video data; and one or more processors implementedin circuitry and configured to: generate an intra-prediction block for acurrent block of video data using an angular intra-prediction mode, theangular intra-prediction mode being an upper-right angularintra-prediction mode or a lower-left angular intra-prediction mode;determine a prediction direction of the angular intra-prediction mode;for at least one sample of the intra-prediction block for the currentblock: calculate a gradient term for the at least one sample along theprediction direction; and combine a value of an intra-predicted sampleof the intra-prediction block at a position of the at least one sampleof the intra-prediction block with the gradient term to produce a valueof the at least one sample of the intra-prediction block; and decode thecurrent block using the intra-prediction block.

In another example, a device for decoding video data includes means forgenerating an intra-prediction block for a current block of video datausing an angular intra-prediction mode, the angular intra-predictionmode being an upper-right angular intra-prediction mode or a lower-leftangular intra-prediction mode; means for determining a predictiondirection of the angular intra-prediction mode; means for calculating agradient term for the at least one sample along the prediction directionfor at least one sample of the intra-prediction block for the currentblock; means for combining a value of an intra-predicted sample of theintra-prediction block at a position of the at least one sample of theintra-prediction block with the gradient term to produce a value of theat least one sample of the intra-prediction block for the at least onesample of the intra-prediction block for the current block; and meansfor decoding the current block using the intra-prediction block.

In another example, a computer-readable storage medium has storedthereon instructions that, when executed, cause a processor to generatean intra-prediction block for a current block of video data using anangular intra-prediction mode, the angular intra-prediction mode beingan upper-right angular intra-prediction mode or a lower-left angularintra-prediction mode; determine a prediction direction of the angularintra-prediction mode; for at least one sample of the intra-predictionblock for the current block: calculate a gradient term for the at leastone sample along the prediction direction; and combine a value of anintra-predicted sample of the intra-prediction block at a position ofthe at least one sample of the intra-prediction block with the gradientterm to produce a value of the at least one sample of theintra-prediction block; and decode the current block using theintra-prediction block.

The details of one or more examples are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description, drawings, and claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a conceptual diagram illustrating example intra-predictionmodes that may be used when performing the techniques of thisdisclosure.

FIG. 2 is a conceptual diagram illustrating position-dependentintra-prediction combination (PDPC) for an intra-prediction mode for annScale value greater than or equal to zero that may be used whenperforming the techniques of this disclosure.

FIG. 3 is a conceptual diagram illustrating an example in which annScale value for a block indicates that position-dependentintra-prediction combination (PDPC) is not to be applied to the blockthat may be used when performing the techniques of this disclosure.

FIG. 4 is a conceptual diagram illustrating nScale values as a functionof a height of a transform block (nTbH) and a mode number that may beused when performing the techniques of this disclosure.

FIG. 5 is a block diagram illustrating an example video encoding anddecoding system that may perform the techniques of this disclosure.

FIG. 6 is a conceptual diagram illustrating an example set of data thatmay be used to perform a gradient position-dependent intra-predictioncombination (PDPC) for a given intra-prediction angle using thetechniques of this disclosure.

FIG. 7 is a conceptual diagram illustrating an example set of data thatmay be used for gradient position-dependent intra-prediction combination(PDPC) for vertical mode using the techniques of this disclosure.

FIG. 8 is a block diagram illustrating an example video encoder that mayperform the techniques of this disclosure.

FIG. 9 is a block diagram illustrating an example video decoder that mayperform the techniques of this disclosure.

FIG. 10 is a flowchart illustrating an example method for encoding acurrent block in accordance with the techniques of this disclosure.

FIG. 11 is a flowchart illustrating an example method for decoding acurrent block in accordance with the techniques of this disclosure.

FIG. 12 is a flowchart illustrating an example method of predicting ablock using gradient PDPC according to the techniques of thisdisclosure.

DETAILED DESCRIPTION

Video coding standards include ITU-T H.261, ISO/IEC MPEG-1 Visual, ITU-TH.262 or ISO/IEC MPEG-2 Visual, ITU-T H.263, ISO/IEC MPEG-4 Visual(MPEG-4 Part 2), ITU-T H.264 (also known as ISO/IEC MPEG-4 AVC),including its Scalable Video Coding (SVC) and Multiview Video Coding(MVC) extensions, and ITU-T H.265 (also known as ISO/IEC MPEG-4 HEVC(High Efficiency Video Coding)) with its extensions. During the April2018 meeting of the Joint Video Experts Team (JVET), the Versatile VideoCoding (VVC) standardization activity (also known as ITU-T H.266) began,with evaluation of video compression technologies submitted to a Callfor Proposals. The techniques of this disclosure may be applied to othervideo coding standards, such as Essential Video Coding (EVC), “Text ofISO/IEC CD 23094-1, Essential Video Coding,” MPEG-5, ISO/IEC CD 23094-1,Jul. 22, 2019, available atmpeg.chiariglione.org/standards/mpeg-5/essential-video-coding/text-isoiec-cd-23094-1-essential-video-coding.

FIG. 1 is a conceptual diagram illustrating example intra-predictionmodes that may be used when performing the techniques of thisdisclosure. The modes of FIG. 1 correspond to an example of modes inVersatile Video Coding (VVC) Test Model (VTM) 7.0. To capture thearbitrary edge directions presented in natural video, the number ofdirectional intra modes in VTM5 is extended from 33, as used in HEVC, to65. The new directional modes in VVC are depicted in graph 8 of FIG. 1 ,and the planar and DC modes remain the same as in HEVC. These denserdirectional intra-prediction modes apply for all block sizes and forboth luma and chroma intra-predictions. Such is explained in J. Chen, Y.Ye, S. Kim, “Algorithm description for Versatile Video Coding and TestModel 7 (VTM5),” 16^(th) JVET Meeting, Geneva, CH, October 2019,JVET-P1002.

In VVC, position-dependent intra-prediction combination (PDPC) is anintra-prediction method applied to a current block (e.g., a luma orchroma component), by which a video coder (encoder or decoder) combinesan original intra-prediction signal with boundary reference samples(which may be unfiltered or filtered) to generate a final predictionsignal for the current block. According to VVC, the video coder appliesPDPC to the following intra modes without signalling: planar, DC,horizontal, vertical, and angular modes with positive angles (modeshaving mode number less than 18 or greater than 50). Such is furtherexplained in B. Bross, J. Chen, S. Liu, “Versatile Video Coding (Draft7),” 16th JVET Meeting, Geneva, CH, March 2019, JVET-P1001.

FIG. 2 is a conceptual diagram illustrating position-dependentintra-prediction combination (PDPC) for an intra-prediction mode for annScale value greater than or equal to zero that may be used whenperforming the techniques of this disclosure. In particular, FIG. 2illustrates a current block 10 including intra-prediction sample 12.Intra-prediction sample 12 is at position (x,y) in this example, wherean upper-left intra-prediction sample of current block 10 is at position(0,0). As shown in FIG. 2 , for angular intra-prediction modes, for agiven intra-prediction direction (indicated by arrow 14), referencepixel 16 (at position r(x+d, −1) in FIG. 2 ) for intra-prediction sample12 is derived from the top reference line (i.e., the line of samplesimmediately above current block 10). For PDPC, the diagonally oppositereference pixel is reference pixel 18 (at position r(−1, y+d1) in FIG. 2) along the prediction direction for the prediction of pixels at (x,y)position that is used for the prediction combinations. However,depending on the coding unit (CU) dimension and prediction direction,the diagonally opposite reference pixels may not necessarily beavailable. Such unavailable reference pixels may be referred to as beingoutside of “PDPC range.” According to conventional VVC, PDPC cannot beapplied in such cases.

FIG. 3 is a conceptual diagram illustrating a scenario in which annScale value for block 20 indicates that position-dependentintra-prediction combination (PDPC) is not to be applied to block 20,which may be used when performing the techniques of this disclosure. InVTM-7.0, “PDPC range” is not checked explicitly for every pixel.Instead, a video coder modifies the factor “nScale” to be derived fromthe prediction direction (invAngle) and block dimension, whichautomatically specifies the “PDPC range” or the region where PDPC shouldbe applied, as explained in F. Bossen, “On general intra sampleprediction”, 15th JVET Meeting, Gothenburg, SE, July 2019, JVET-00364.With this modification, the video coder applies PDPC for (x<(3<<nScale))OR (y<(3<<nScale)), depending on whether the mode number is greater than50 or less than 18. As a consequence, when (nScale<0) PDPC is notapplied (which is shown in FIG. 3 , for a given prediction direction 22for bottom-left pixel 24 inside block 20), the diagonally oppositereference pixel is not available. Thus, using the conventionaltechniques of VVC, PDPC cannot be applied, even for the pixels in firstcolumn of the block.

FIG. 4 is a conceptual diagram illustrating graph 30 including nScalevalues as a function of a height of a transform block (nTbH) and a modenumber that may be used when performing the techniques of thisdisclosure. For some prediction directions and block dimensions, PDPC isnot applied for nScale<0. The nScale values for different predictiondirection (indicated by mode number) and block dimension (e.g.,transform block (TB) size) are shown in FIG. 4 . This disclosuredescribes various alternative ways of computing PDPC, which may lead tobetter compression performance for those cases.

FIG. 5 is a block diagram illustrating an example video encoding anddecoding system 100 that may perform the techniques of this disclosure.The techniques of this disclosure are generally directed to coding(encoding and/or decoding) video data. In general, video data includesany data for processing a video. Thus, video data may include raw,uncoded video, encoded video, decoded (e.g., reconstructed) video, andvideo metadata, such as signaling data.

As shown in FIG. 5 , system 100 includes a source device 102 thatprovides encoded video data to be decoded and displayed by a destinationdevice 116, in this example. In particular, source device 102 providesthe video data to destination device 116 via a computer-readable medium110. Source device 102 and destination device 116 may comprise any of awide range of devices, including desktop computers, notebook (i.e.,laptop) computers, tablet computers, set-top boxes, telephone handsetssuch as smartphones, televisions, cameras, display devices, digitalmedia players, video gaming consoles, video streaming device, or thelike. In some cases, source device 102 and destination device 116 may beequipped for wireless communication, and thus may be referred to aswireless communication devices.

In the example of FIG. 5 , source device 102 includes video source 104,memory 106, video encoder 200, and output interface 108. Destinationdevice 116 includes input interface 122, video decoder 300, memory 120,and display device 118. In accordance with this disclosure, videoencoder 200 of source device 102 and video decoder 300 of destinationdevice 116 may be configured to apply the techniques for performingposition-dependent intra-prediction combination (PDPC) for angularintra-prediction modes. Thus, source device 102 represents an example ofa video encoding device, while destination device 116 represents anexample of a video decoding device. In other examples, a source deviceand a destination device may include other components or arrangements.For example, source device 102 may receive video data from an externalvideo source, such as an external camera. Likewise, destination device116 may interface with an external display device, rather than includingan integrated display device.

System 100 as shown in FIG. 5 is merely one example. In general, anydigital video encoding and/or decoding device may perform techniques forperforming position-dependent intra-prediction combination (PDPC) forangular intra-prediction modes. Source device 102 and destination device116 are merely examples of such coding devices in which source device102 generates coded video data for transmission to destination device116. This disclosure refers to a “coding” device as a device thatperforms coding (encoding and/or decoding) of data. Thus, video encoder200 and video decoder 300 represent examples of coding devices, inparticular, a video encoder and a video decoder, respectively. In someexamples, source device 102 and destination device 116 may operate in asubstantially symmetrical manner such that each of source device 102 anddestination device 116 include video encoding and decoding components.Hence, system 100 may support one-way or two-way video transmissionbetween source device 102 and destination device 116, e.g., for videostreaming, video playback, video broadcasting, or video telephony.

In general, video source 104 represents a source of video data (i.e.,raw, uncoded video data) and provides a sequential series of pictures(also referred to as “frames”) of the video data to video encoder 200,which encodes data for the pictures. Video source 104 of source device102 may include a video capture device, such as a video camera, a videoarchive containing previously captured raw video, and/or a video feedinterface to receive video from a video content provider. As a furtheralternative, video source 104 may generate computer graphics-based dataas the source video, or a combination of live video, archived video, andcomputer-generated video. In each case, video encoder 200 encodes thecaptured, pre-captured, or computer-generated video data. Video encoder200 may rearrange the pictures from the received order (sometimesreferred to as “display order”) into a coding order for coding. Videoencoder 200 may generate a bitstream including encoded video data.Source device 102 may then output the encoded video data via outputinterface 108 onto computer-readable medium 110 for reception and/orretrieval by, e.g., input interface 122 of destination device 116.

Memory 106 of source device 102 and memory 120 of destination device 116represent general purpose memories. In some examples, memories 106, 120may store raw video data, e.g., raw video from video source 104 and raw,decoded video data from video decoder 300. Additionally oralternatively, memories 106, 120 may store software instructionsexecutable by, e.g., video encoder 200 and video decoder 300,respectively. Although shown separately from video encoder 200 and videodecoder 300 in this example, it should be understood that video encoder200 and video decoder 300 may also include internal memories forfunctionally similar or equivalent purposes. Furthermore, memories 106,120 may store encoded video data, e.g., output from video encoder 200and input to video decoder 300. In some examples, portions of memories106, 120 may be allocated as one or more video buffers, e.g., to storeraw, decoded, and/or encoded video data.

Computer-readable medium 110 may represent any type of medium or devicecapable of transporting the encoded video data from source device 102 todestination device 116. In one example, computer-readable medium 110represents a communication medium to enable source device 102 totransmit encoded video data directly to destination device 116 inreal-time, e.g., via a radio frequency network or computer-basednetwork. Output interface 108 may modulate a transmission signalincluding the encoded video data, and input interface 122 may demodulatethe received transmission signal, according to a communication standard,such as a wireless communication protocol. The communication medium maycomprise any wireless or wired communication medium, such as a radiofrequency (RF) spectrum or one or more physical transmission lines. Thecommunication medium may form part of a packet-based network, such as alocal area network, a wide-area network, or a global network such as theInternet. The communication medium may include routers, switches, basestations, or any other equipment that may be useful to facilitatecommunication from source device 102 to destination device 116.

In some examples, source device 102 may output encoded data from outputinterface 108 to storage device 112. Similarly, destination device 116may access encoded data from storage device 112 via input interface 122.Storage device 112 may include any of a variety of distributed orlocally accessed data storage media such as a hard drive, Blu-ray discs,DVDs, CD-ROMs, flash memory, volatile or non-volatile memory, or anyother suitable digital storage media for storing encoded video data.

In some examples, source device 102 may output encoded video data tofile server 114 or another intermediate storage device that may storethe encoded video generated by source device 102. Destination device 116may access stored video data from file server 114 via streaming ordownload. File server 114 may be any type of server device capable ofstoring encoded video data and transmitting that encoded video data tothe destination device 116. File server 114 may represent a web server(e.g., for a website), a File Transfer Protocol (FTP) server, a contentdelivery network device, or a network attached storage (NAS) device.Destination device 116 may access encoded video data from file server114 through any standard data connection, including an Internetconnection. This may include a wireless channel (e.g., a Wi-Ficonnection), a wired connection (e.g., digital subscriber line (DSL),cable modem, etc.), or a combination of both that is suitable foraccessing encoded video data stored on file server 114. File server 114and input interface 122 may be configured to operate according to astreaming transmission protocol, a download transmission protocol, or acombination thereof.

Output interface 108 and input interface 122 may represent wirelesstransmitters/receivers, modems, wired networking components (e.g.,Ethernet cards), wireless communication components that operateaccording to any of a variety of IEEE 802.11 standards, or otherphysical components. In examples where output interface 108 and inputinterface 122 comprise wireless components, output interface 108 andinput interface 122 may be configured to transfer data, such as encodedvideo data, according to a cellular communication standard, such as 4G,4G-LTE (Long-Term Evolution), LTE Advanced, 5G, or the like. In someexamples where output interface 108 comprises a wireless transmitter,output interface 108 and input interface 122 may be configured totransfer data, such as encoded video data, according to other wirelessstandards, such as an IEEE 802.11 specification, an IEEE 802.15specification (e.g., ZigBee™), a Bluetooth™ standard, or the like. Insome examples, source device 102 and/or destination device 116 mayinclude respective system-on-a-chip (SoC) devices. For example, sourcedevice 102 may include an SoC device to perform the functionalityattributed to video encoder 200 and/or output interface 108, anddestination device 116 may include an SoC device to perform thefunctionality attributed to video decoder 300 and/or input interface122.

The techniques of this disclosure may be applied to video coding insupport of any of a variety of multimedia applications, such asover-the-air television broadcasts, cable television transmissions,satellite television transmissions, Internet streaming videotransmissions, such as dynamic adaptive streaming over HTTP (DASH),digital video that is encoded onto a data storage medium, decoding ofdigital video stored on a data storage medium, or other applications.

Input interface 122 of destination device 116 receives an encoded videobitstream from computer-readable medium 110 (e.g., storage device 112,file server 114, or the like). The encoded video bitstream may includesignaling information defined by video encoder 200, which is also usedby video decoder 300, such as syntax elements having values thatdescribe characteristics and/or processing of video blocks or othercoded units (e.g., slices, pictures, groups of pictures, sequences, orthe like). Display device 118 displays decoded pictures of the decodedvideo data to a user. Display device 118 may represent any of a varietyof display devices such as a cathode ray tube (CRT), a liquid crystaldisplay (LCD), a plasma display, an organic light emitting diode (OLED)display, or another type of display device.

Although not shown in FIG. 5 , in some examples, video encoder 200 andvideo decoder 300 may each be integrated with an audio encoder and/oraudio decoder, and may include appropriate MUX-DEMUX units, or otherhardware and/or software, to handle multiplexed streams including bothaudio and video in a common data stream. If applicable, MUX-DEMUX unitsmay conform to the ITU H.223 multiplexer protocol, or other protocolssuch as the user datagram protocol (UDP).

Video encoder 200 and video decoder 300 each may be implemented as anyof a variety of suitable encoder and/or decoder circuitry, such as oneor more microprocessors, digital signal processors (DSPs), applicationspecific integrated circuits (ASICs), field programmable gate arrays(FPGAs), discrete logic, software, hardware, firmware or anycombinations thereof. When the techniques are implemented partially insoftware, a device may store instructions for the software in asuitable, non-transitory computer-readable medium and execute theinstructions in hardware using one or more processors to perform thetechniques of this disclosure. Each of video encoder 200 and videodecoder 300 may be included in one or more encoders or decoders, eitherof which may be integrated as part of a combined encoder/decoder (CODEC)in a respective device. A device including video encoder 200 and/orvideo decoder 300 may comprise an integrated circuit, a microprocessor,and/or a wireless communication device, such as a cellular telephone.

Video encoder 200 and video decoder 300 may operate according to a videocoding standard, such as ITU-T H.265, also referred to as HighEfficiency Video Coding (HEVC) or extensions thereto, such as themulti-view and/or scalable video coding extensions. Alternatively, videoencoder 200 and video decoder 300 may operate according to otherproprietary or industry standards, such as the Joint Exploration TestModel (JEM) or ITU-T H.266, also referred to as Versatile Video Coding(VVC). The techniques of this disclosure, however, are not limited toany particular coding standard.

In general, video encoder 200 and video decoder 300 may performblock-based coding of pictures. The term “block” generally refers to astructure including data to be processed (e.g., encoded, decoded, orotherwise used in the encoding and/or decoding process). For example, ablock may include a two-dimensional matrix of samples of luminanceand/or chrominance data. In general, video encoder 200 and video decoder300 may code video data represented in a YUV (e.g., Y, Cb, Cr) format.That is, rather than coding red, green, and blue (RGB) data for samplesof a picture, video encoder 200 and video decoder 300 may code luminanceand chrominance components, where the chrominance components may includeboth red hue and blue hue chrominance components. In some examples,video encoder 200 converts received RGB formatted data to a YUVrepresentation prior to encoding, and video decoder 300 converts the YUVrepresentation to the RGB format. Alternatively, pre- andpost-processing units (not shown) may perform these conversions.

This disclosure may generally refer to coding (e.g., encoding anddecoding) of pictures to include the process of encoding or decodingdata of the picture. Similarly, this disclosure may refer to coding ofblocks of a picture to include the process of encoding or decoding datafor the blocks, e.g., prediction and/or residual coding. An encodedvideo bitstream generally includes a series of values for syntaxelements representative of coding decisions (e.g., coding modes) andpartitioning of pictures into blocks. Thus, references to coding apicture or a block should generally be understood as coding values forsyntax elements forming the picture or block.

HEVC defines various blocks, including coding units (CUs), predictionunits (PUs), and transform units (TUs). According to HEVC, a video coder(such as video encoder 200) partitions a coding tree unit (CTU) into CUsaccording to a quadtree structure. That is, the video coder partitionsCTUs and CUs into four equal, non-overlapping squares, and each node ofthe quadtree has either zero or four child nodes. Nodes without childnodes may be referred to as “leaf nodes,” and CUs of such leaf nodes mayinclude one or more PUs and/or one or more TUs. The video coder mayfurther partition PUs and TUs. For example, in HEVC, a residual quadtree(RQT) represents partitioning of TUs. In HEVC, PUs representinter-prediction data, while TUs represent residual data. CUs that areintra-predicted include intra-prediction information, such as anintra-mode indication.

As another example, video encoder 200 and video decoder 300 may beconfigured to operate according to JEM or VVC. According to JEM or VVC,a video coder (such as video encoder 200) partitions a picture into aplurality of coding tree units (CTUs). Video encoder 200 may partition aCTU according to a tree structure, such as a quadtree-binary tree (QTBT)structure or Multi-Type Tree (MTT) structure. The QTBT structure removesthe concepts of multiple partition types, such as the separation betweenCUs, PUs, and TUs of HEVC. A QTBT structure includes two levels: a firstlevel partitioned according to quadtree partitioning, and a second levelpartitioned according to binary tree partitioning. A root node of theQTBT structure corresponds to a CTU. Leaf nodes of the binary treescorrespond to coding units (CUs).

In an MTT partitioning structure, blocks may be partitioned using aquadtree (QT) partition, a binary tree (BT) partition, and one or moretypes of triple tree (TT) partitions. A triple tree partition is apartition where a block is split into three sub-blocks. In someexamples, a triple tree partition divides a block into three sub-blockswithout dividing the original block through the center. The partitioningtypes in MTT (e.g., QT, BT, and TT), may be symmetrical or asymmetrical.

In some examples, video encoder 200 and video decoder 300 may use asingle QTBT or MTT structure to represent each of the luminance andchrominance components, while in other examples, video encoder 200 andvideo decoder 300 may use two or more QTBT or MTT structures, such asone QTBT/MTT structure for the luminance component and another QTBT/MTTstructure for both chrominance components (or two QTBT/MTT structuresfor respective chrominance components).

Video encoder 200 and video decoder 300 may be configured to usequadtree partitioning per HEVC, QTBT partitioning, MTT partitioning, orother partitioning structures. For purposes of explanation, thedescription of the techniques of this disclosure is presented withrespect to QTBT partitioning. However, it should be understood that thetechniques of this disclosure may also be applied to video codersconfigured to use quadtree partitioning, or other types of partitioningas well.

The blocks (e.g., CTUs or CUs) may be grouped in various ways in apicture. As one example, a brick may refer to a rectangular region ofCTU rows within a particular tile in a picture. A tile may be arectangular region of CTUs within a particular tile column and aparticular tile row in a picture. A tile column refers to a rectangularregion of CTUs having a height equal to the height of the picture and awidth specified by syntax elements (e.g., such as in a picture parameterset). A tile row refers to a rectangular region of CTUs having a heightspecified by syntax elements (e.g., such as in a picture parameter set)and a width equal to the width of the picture.

In some examples, a tile may be partitioned into multiple bricks, eachof which may include one or more CTU rows within the tile. A tile thatis not partitioned into multiple bricks may also be referred to as abrick. However, a brick that is a true subset of a tile may not bereferred to as a tile.

The bricks in a picture may also be arranged in a slice. A slice may bean integer number of bricks of a picture that may be exclusivelycontained in a single network abstraction layer (NAL) unit. In someexamples, a slice includes either a number of complete tiles or only aconsecutive sequence of complete bricks of one tile.

This disclosure may use “N×N” and “N by N” interchangeably to refer tothe sample dimensions of a block (such as a CU or other video block) interms of vertical and horizontal dimensions, e.g., 16×16 samples or 16by 16 samples. In general, a 16×16 CU will have 16 samples in a verticaldirection (y=16) and 16 samples in a horizontal direction (x=16).Likewise, an N×N CU generally has N samples in a vertical direction andN samples in a horizontal direction, where N represents a nonnegativeinteger value. The samples in a CU may be arranged in rows and columns.Moreover, CUs need not necessarily have the same number of samples inthe horizontal direction as in the vertical direction. For example, CUsmay comprise N×M samples, where M is not necessarily equal to N.

Video encoder 200 encodes video data for CUs representing predictionand/or residual information, and other information. The predictioninformation indicates how the CU is to be predicted in order to form aprediction block for the CU. The residual information generallyrepresents sample-by-sample differences between samples of the CU priorto encoding and the prediction block.

To predict a CU, video encoder 200 may generally form a prediction blockfor the CU through inter-prediction or intra-prediction.Inter-prediction generally refers to predicting the CU from data of apreviously coded picture, whereas intra-prediction generally refers topredicting the CU from previously coded data of the same picture. Toperform inter-prediction, video encoder 200 may generate the predictionblock using one or more motion vectors. Video encoder 200 may generallyperform a motion search to identify a reference block that closelymatches the CU, e.g., in terms of differences between the CU and thereference block. Video encoder 200 may calculate a difference metricusing a sum of absolute difference (SAD), sum of squared differences(SSD), mean absolute difference (MAD), mean squared differences (MSD),or other such difference calculations to determine whether a referenceblock closely matches the current CU. In some examples, video encoder200 may predict the current CU using uni-directional prediction orbi-directional prediction.

Some examples of JEM and VVC also provide an affine motion compensationmode, which may be considered an inter-prediction mode. In affine motioncompensation mode, video encoder 200 may determine two or more motionvectors that represent non-translational motion, such as zoom in or out,rotation, perspective motion, or other irregular motion types.

To perform intra-prediction, video encoder 200 may select anintra-prediction mode to generate the prediction block. Some examples ofJEM and VVC provide sixty-seven intra-prediction modes, includingvarious directional modes, as well as planar mode and DC mode. Ingeneral, video encoder 200 selects an intra-prediction mode thatdescribes neighboring samples to a current block (e.g., a block of a CU)from which to predict samples of the current block. Such samples maygenerally be above, above and to the left, or to the left of the currentblock in the same picture as the current block, assuming video encoder200 codes CTUs and CUs in raster scan order (left to right, top tobottom).

Video encoder 200 encodes data representing the prediction mode for acurrent block. For example, for inter-prediction modes, video encoder200 may encode data representing which of the various availableinter-prediction modes is used, as well as motion information for thecorresponding mode. For uni-directional or bi-directionalinter-prediction, for example, video encoder 200 may encode motionvectors using advanced motion vector prediction (AMVP) or merge mode.Video encoder 200 may use similar modes to encode motion vectors foraffine motion compensation mode.

In some examples, video encoder 200 (and similarly, video decoder 300)may perform position-dependent intra-prediction combination (PDPC) for acurrent block of video data. As discussed above, conventionally, PDPCincludes combining a standard intra-predicted block with values fromneighboring reference pixels (or samples) along the intra-predictiondirection, e.g., from an opposite boundary. According to the techniquesof this disclosure, in cases where PDPC cannot be applied conventionallydue to reference pixels being outside of the PDPC range, video encoder200 and video decoder 300 may alternatively compute PDPC for angularmodes using “gradient PDPC.” These techniques may generally be performedfor two cases (although other cases may exist as well): Case 1 in whichan intra-prediction mode is an upper-right angular intra-prediction mode(e.g., modes labeled 51-80 in FIG. 1 , that is, modes greater than 50and less than 81) and Case 2 in which the intra-prediction mode is alower-left angular intra-prediction mode (e.g., modes labeled less than18, excluding DC and planar modes (0 and 1, respectively) in FIG. 1 ).Gradient PDPC is explained in greater detail below with respect to FIG.6 .

In general, PDPC involves forming a prediction block for a current blockusing samples of a primary boundary and a secondary boundary. However,the two cases above represent angular modes for which samples of thesecondary boundary are not available. Therefore, video encoder 200 andvideo decoder 300 may calculate a gradient term for one or more samplesof the current block along a prediction direction (angle) for theintra-prediction modes. Video encoder 200 and video decoder 300 may thencombine a value predicted using the primary boundary with the gradientterm to form the predicted sample of a prediction block for the currentblock. Video encoder 200 and video decoder 300 may calculate thegradient term using a displacement value according to the angle of thecorresponding intra-prediction mode. In some examples, video encoder 200and video decoder 300 may weight the value predicted using the primaryboundary and the gradient term, e.g., according to a distance betweenthe position of the sample being predicted and a horizontally orvertically neighboring reference pixel.

Following prediction, such as intra-prediction using a gradient PDPCmode according to the techniques of this disclosure, video encoder 200may calculate residual data for the block. The residual data, such as aresidual block, represents sample by sample differences between theblock and a prediction block for the block, formed using thecorresponding prediction mode. Video encoder 200 may apply one or moretransforms to the residual block, to produce transformed data in atransform domain instead of the sample domain. For example, videoencoder 200 may apply a discrete cosine transform (DCT), an integertransform, a wavelet transform, or a conceptually similar transform toresidual video data. Additionally, video encoder 200 may apply asecondary transform following the first transform, such as amode-dependent non-separable secondary transform (MDNSST), a signaldependent transform, a Karhunen-Loeve transform (KLT), or the like.Video encoder 200 produces transform coefficients following applicationof the one or more transforms.

As noted above, following any transforms to produce transformcoefficients, video encoder 200 may perform quantization of thetransform coefficients. Quantization generally refers to a process inwhich transform coefficients are quantized to possibly reduce the amountof data used to represent the coefficients, providing furthercompression. By performing the quantization process, video encoder 200may reduce the bit depth associated with some or all of thecoefficients. For example, video encoder 200 may round an n-bit valuedown to an m-bit value during quantization, where n is greater than m.In some examples, to perform quantization, video encoder 200 may performa bitwise right-shift of the value to be quantized.

Following quantization, video encoder 200 may scan the transformcoefficients, producing a one-dimensional vector from thetwo-dimensional matrix including the quantized transform coefficients.The scan may be designed to place higher energy (and therefore lowerfrequency) coefficients at the front of the vector and to place lowerenergy (and therefore higher frequency) transform coefficients at theback of the vector. In some examples, video encoder 200 may utilize apredefined scan order to scan the quantized transform coefficients toproduce a serialized vector, and then entropy encode the quantizedtransform coefficients of the vector. In other examples, video encoder200 may perform an adaptive scan. After scanning the quantized transformcoefficients to form the one-dimensional vector, video encoder 200 mayentropy encode the one-dimensional vector, e.g., according tocontext-adaptive binary arithmetic coding (CABAC). Video encoder 200 mayalso entropy encode values for syntax elements describing metadataassociated with the encoded video data for use by video decoder 300 indecoding the video data.

To perform CABAC, video encoder 200 may assign a context within acontext model to a symbol to be transmitted. The context may relate to,for example, whether neighboring values of the symbol are zero-valued ornot. The probability determination may be based on a context assigned tothe symbol.

Video encoder 200 may further generate syntax data, such as block-basedsyntax data, picture-based syntax data, and sequence-based syntax data,to video decoder 300, e.g., in a picture header, a block header, a sliceheader, or other syntax data, such as a sequence parameter set (SPS),picture parameter set (PPS), or video parameter set (VPS). Video decoder300 may likewise decode such syntax data to determine how to decodecorresponding video data. In some examples, video encoder 200 mayencode, and video decoder 300 may decode, syntax data of a VPS, SPS,PPS, or other such data structure (e.g., a picture header, a sliceheader, a block header, or the like) related to gradient PDPC. Forexample, the syntax data may represent whether gradient PDPC is enabled,values used to determine angular intra-prediction modes for whichgradient PDPC is enabled and to be used, or the like.

In this manner, video encoder 200 may generate a bitstream includingencoded video data, e.g., syntax elements describing partitioning of apicture into blocks (e.g., CUs) and prediction and/or residualinformation for the blocks. Ultimately, video decoder 300 may receivethe bitstream and decode the encoded video data.

In general, video decoder 300 performs a reciprocal process to thatperformed by video encoder 200 to decode the encoded video data of thebitstream. For example, video decoder 300 may decode values for syntaxelements of the bitstream using CABAC in a manner substantially similarto, albeit reciprocal to, the CABAC encoding process of video encoder200. The syntax elements may define partitioning information of apicture into CTUs, and partitioning of each CTU according to acorresponding partition structure, such as a QTBT structure, to defineCUs of the CTU. The syntax elements may further define prediction andresidual information for blocks (e.g., CUs) of video data.

The residual information may be represented by, for example, quantizedtransform coefficients. Video decoder 300 may inverse quantize andinverse transform the quantized transform coefficients of a block toreproduce a residual block for the block. Video decoder 300 uses asignaled prediction mode (intra- or inter-prediction) and relatedprediction information (e.g., motion information for inter-prediction)to form a prediction block for the block. Video decoder 300 may thencombine the prediction block and the residual block (on asample-by-sample basis) to reproduce the original block. Video decoder300 may perform additional processing, such as performing a deblockingprocess to reduce visual artifacts along boundaries of the block.

This disclosure may generally refer to “signaling” certain information,such as syntax elements. The term “signaling” may generally refer to thecommunication of values for syntax elements and/or other data used todecode encoded video data. That is, video encoder 200 may signal valuesfor syntax elements in the bitstream. In general, signaling refers togenerating a value in the bitstream. As noted above, source device 102may transport the bitstream to destination device 116 substantially inreal time, or not in real time, such as might occur when storing syntaxelements to storage device 112 for later retrieval by destination device116.

In VVC, CUs may be split using quadtree splitting, binary treesplitting, and/or center-side triple splitting. In each split (i.e.,non-leaf) node of the binary tree, one flag may be signaled to indicatewhich splitting type (i.e., horizontal or vertical) is used, where 0 mayindicate horizontal splitting and 1 may indicate vertical splitting. Forquadtree splitting, there is no need to indicate the splitting type,since quadtree nodes split a block horizontally and vertically into 4sub-blocks with equal size. Accordingly, video encoder 200 may encode,and video decoder 300 may decode, syntax elements (such as splittinginformation) for a region tree level of a QTBT structure and syntaxelements (such as splitting information) for a prediction tree level ofthe QTBT structure. Video encoder 200 may encode, and video decoder 300may decode, video data, such as prediction and transform data, for CUsrepresented by terminal leaf nodes of the QTBT structure.

In general, a CTU may be associated with parameters defining sizes ofblocks corresponding to nodes of a QTBT structure at the first andsecond levels. These parameters may include a CTU size (representing asize of the CTU in samples), a minimum quadtree size (MinQTSize,representing a minimum allowed quadtree leaf node size), a maximumbinary tree size (MaxBTSize, representing a maximum allowed binary treeroot node size), a maximum binary tree depth (MaxBTDepth, representing amaximum allowed binary tree depth), and a minimum binary tree size(MinBTSize, representing the minimum allowed binary tree leaf nodesize).

The root node of a QTBT structure corresponding to a CTU may have fourchild nodes at the first level of the QTBT structure, each of which maybe partitioned according to quadtree partitioning. That is, nodes of thefirst level are either leaf nodes (having no child nodes) or have fourchild nodes. If nodes of the first level are not larger than the maximumallowed binary tree root node size (MaxBTSize), they can be furtherpartitioned by respective binary trees. The binary tree splitting of onenode can be iterated until the nodes resulting from the split reach theminimum allowed binary tree leaf node size (MinBTSize) or the maximumallowed binary tree depth (MaxBTDepth). The binary tree leaf node isreferred to as a coding unit (CU), which is used for prediction (e.g.,intra-picture or inter-picture prediction) and transform, without anyfurther partitioning. As discussed above, CUs may also be referred to as“video blocks” or “blocks.”

In one example of the QTBT partitioning structure, the CTU size is setas 128×128 (luma samples and two corresponding 64×64 chroma samples),the MinQTSize is set as 16×16, the MaxBTSize is set as 64×64, theMinBTSize (for both width and height) is set as 4, and the MaxBTDepth isset as 4. The quadtree partitioning is applied to the CTU first togenerate quad-tree leaf nodes. The quadtree leaf nodes may have a sizefrom 16×16 (i.e., the MinQTSize) to 128×128 (i.e., the CTU size). If theleaf quadtree node is 128×128, it will not be further split by thebinary tree, since the size exceeds the MaxBTSize (i.e., 64×64, in thisexample). Otherwise, the leaf quadtree node will be further partitionedby the binary tree. Therefore, the quadtree leaf node is also the rootnode for the binary tree and has the binary tree depth as 0. When thebinary tree depth reaches MaxBTDepth (4, in this example), no furthersplitting is permitted. When the binary tree node has width equal toMinBTSize (4, in this example), it implies no further horizontalsplitting is permitted. Similarly, a binary tree node having a heightequal to MinBTSize implies no further vertical splitting is permittedfor that binary tree node. As noted above, leaf nodes of the binary treeare referred to as CUs, and are further processed according toprediction and transform without further partitioning.

FIG. 6 is a conceptual diagram illustrating an example set of data thatmay be used to perform a gradient position-dependent intra-predictioncombination (PDPC) for a given intra-prediction angle using thetechniques of this disclosure. FIG. 6 illustrates current block 140including intra-prediction sample 142. To perform gradient PDPC, videoencoder 200 or video decoder 300 may compute the intensity variation or“gradient” along the prediction direction, as shown by arrow 144 in FIG.6 (for Case 1, i.e., an upper-right intra-prediction direction). ForCase 1, for a sample at position (x,y) (e.g., intra-prediction sample142), video encoder 200 and video decoder 300 may fetch a value ofhorizontally-aligned reference sample 146 (at position r(−1, y)), fromthe left reference line to current block 140. To compute the gradientalong this prediction direction and offset (straight line with slopesame as prediction direction and containing sample r(−1,y)), videoencoder 200 and video decoder 300 may derive a value for thecorresponding pixel in the top reference line, e.g., reference sample148 (at position r(−1+d, −1) in FIG. 6 ).

Similarly, for Case 2, for a sample at position (x,y), video encoder 200and video decoder 300 may fetch a value for a vertically alignedreference sample (at position r(x, −1)). To compute the gradient alongthis prediction direction and offset (straight line with slope being thesame as the prediction direction and containing the sample at positionr(x, −1)), video encoder 200 and video decoder 300 may derive thecorresponding pixels in the left reference line, i.e., r(−1, −1+d).

As shown in FIG. 6 , “d” indicates horizontal/x (for Case 1) orvertical/y (for Case 2) displacement compared to the other referencepixel (r(−1,y) for Case 1 or r(x, −1) for Case 2). VVC describes theprocess for calculating the value of d. Video encoder 200 and videodecoder 300 may calculate the value of d prior to the originalprediction process using the intra-prediction angle. “d” may havenon-integer (fractional) values. In VVC, the values of “d” are derivedin 1/32-pixel accuracy (so, for an integer pixel displacement, “d” maybe a multiple of 32). Video encoder 200 and video decoder 300 may derivethe integer (dInt) and fractional (dFrac) (in 1/32-pixel accuracy) pixeldisplacement using:

dInt=d>>5;

dFrac=d&31.

Video encoder 200 and video decoder 300 may apply a variety of differenttechniques to calculate r(−1+d, −1) (for Case 1) or r(−1, −1+d) (forCase 2) for fractional pixel positions. Function Q(i) may refer tor(−1+i, −1) for Case 1 and r(−1, −1+i) for Case 2. To calculate Q(i),video encoder 200 and video decoder 300 may apply any of the followingexample techniques:

-   -   a) Nearest integer pixel (rounding): Q(d)=Q(dRound), where        dRound=(d+16)>>5.    -   b) Linear interpolation (2 tap filtering):        Q(d)=((32−dFrac)*Q(dInt)+dFrac*Q(dInt+1)+16)>>5.    -   c) Cubic interpolation as in VVC(4 tap filtering):        Q(d)=(fC[0]*Q[dInt−1]+fC[1]*Q[dInt]+fC[2]*Q[dInt+1]+fC[3]*Q[dInt+2]+32)>>6,        where sum(fC[i])=64.    -   d) Gaussian interpolation as in VVC (4 tap filtering):        Val=(fG[0]*Q[dInt−1]+fG[1]*Q[dInt]+fG[2]*Q[dInt+1]+fG[3]*Q[dInt+2]+32)>>6,        where sum(fG[i])=64.    -   e) A combination of fC and fG, depending on the prediction        direction and block dimension (identically the same or similar        to what is used in reference pixel smoothing for        intra-prediction in VVC).    -   f) In general, any other finite tap filtering can also be used        for interpolation.

For Case 1, video encoder 200 and video decoder 300 may calculate thegradient term as r(−1,y)−r(−1+d, −1). Similarly, for Case 2, videoencoder 200 and video decoder 300 may calculate the gradient term asr(x, −1)−r(−1, −1+d).

For Case 1, video encoder 200 and video decoder 300 may calculate aweight value that depends on the distance between (x,y) and (−1,y),i.e., depending on the value of x. The weight value may be defined aswL[x], which can be exponentially decaying with respect to x. Forexample, video encoder 200 and video decoder 300 may calculatewL[x]=(a>>((x<<1)>>nScale2), where nScale2 can be derived as (floor(log2(nTbH))+floor(log 2(nTbW))−2)>>2, the value of “a” can be a power of 2and less than 64, such as 32, 16, 8, 4, etc. For Case 2, similarly,video encoder 200 and video decoder 300 may calculate weight wT(y),depending on the distance between (x,y) and (x, −1), aswT[y]=(a>>((y<<1)>>nScale2).

Video encoder 200 and video decoder 300 may calculate the finalprediction signal (after PDPC application) as, for example:

-   -   Case 1: Clip(((64−wL(x))*p(x,y)+wL(x)*(r(−1,y)−r(−1+d,        −1))+32)>>6)    -   Case 2: Clip(((64−wT(y))*p(x,y)+wT(y)*(r(x, −1)−r(−1,        −1+d))+32)>>6)

Video encoder 200 and video decoder 300 may be configured to determineclipping ranges using a bitdepth (e.g., the bitdepth currently beingprocessed). For example, for 10 bits, video encoder 200 and videodecoder 300 may clip values to being between 0 and 1023 (2¹⁰−1). Ingeneral, the clipping range may be (2^(bitdepth)−1).

FIG. 7 is a conceptual diagram illustrating an example set of data thatmay be used for gradient position-dependent intra-prediction combination(PDPC) for vertical intra-prediction mode 150 using the techniques ofthis disclosure. In this example, block 158 includes sample 152. Thisdisclosure extends gradient PDPC to angular intra-prediction modes,contrasted with conventional PDPC. FIG. 7 illustrates an example of aspecial case in which d=0. Video encoder 200 or video decoder 300 mayapply PDPC to predict sample 152 using, e.g., samples 154 and 156 thatneighbor block 158, as discussed in greater detail below. Gradient PDPCmay be applied for (x<(3<<nScale2)) for Case 1, and for (y<(3<<nScale2))for Case 2, and the value of nScale2>=0 for all blocks, so PDPC can beapplied (at least partially, for some rows/columns) for all such blocks.Also, the application of PDPC (range) may depend on nScale2. A highervalue of nScale 2 may indicate that PDPC can be applied for a greaternumber of rows/columns.

In some examples, video encoder 200 and video decoder 300 may applygradient PDPC to blocks where nScale<0, or equivalently, to blocks wherethe original PDPC method of VVC cannot be applied. The correspondingspecification changes to JVET-P2001-vE are shown below, where “[added:“added text”] represents additions relative to JVET-P2001-vE:

3.1.1.1 3.1.1.1.1 Position-dependent intra-prediction sample filteringprocess

Inputs to this process are:—

-   -   the intra-prediction mode predModeIntra,    -   a variable nTbW specifying the transform block width,    -   a variable nTbH specifying the transform block height,    -   a variable refW specifying the reference samples width,    -   a variable refH specifying the reference samples height,    -   the predicted samples predSamples[x][y], with x=0 . . . nTbW−1,        y=0 . . . nTbH−1,    -   the neighbouring samples p[x][y], with x=−1, y=−1 . . . refH−1        and x=0 . . . refW−1, y=−1.    -   Outputs of this process are the modified predicted samples        predSamples[x][y] with x=0 . . . nTbW−1, y=0 . . . nTbH−1.

The variable nScale is derived as follows:

-   -   If predModeIntra is greater than INTRA_ANGULAR50, nScale is set        equal to Min(2, Log 2(nTbH)−Floor(Log 2(3*invAngle−2))+8), using        invAngle as specified in clause 8.4.5.2.12.    -   Otherwise, if predModeIntra is less than INTRA_ANGULAR18, not        equal to INTRA_PLANAR and not equal to INTRA_DC, nScale is set        equal to Min(2, Log 2(nTbW)−Floor(Log 2(3*invAngle−2))+8), using        invAngle as specified in clause 8.4.5.2.12.    -   [added: “The variable nScale2 is set to ((Log 2(nTbW)+Log        2(nTbH)−2)>>2).”]

The reference sample arrays mainRef[x] and sideRef[y], with x=0 . . .refW−1 and y=0 . . . refH−1 are derived as follows:

mainRef[x]=p[x][−1]

sideRef[y]=p[−1][y]  (424)

-   -   The variables refL[x][y], refT[x][y], wT[y], and wL[x] with x=0        . . . nTbW−1, y=0 . . . nTbH−1 are derived as follows:    -   If predModeIntra is equal to INTRA_PLANAR or INTRA_DC, the        following applies:

refL[x][y]=p[−1][y]  (425)

refT[x][y]=p[x][−1]  (426)

wT[y]=32>>((y<<1)>>[added: “nScale2”])   (427)

wL[x]=32>>((x<<1)>>[added: “nScale2”])   (428)

-   -   Otherwise, if predModeIntra is equal to INTRA_ANGULAR18 or        INTRA_ANGULAR50 [added: “or nScale is less than 0”], the        following applies:    -   [added: “The variable tempSample is derived, using iIdx and        iFact as specified in clause 8.4.5.2.12, as follows:

If predModeIntra is less than or equal to INTRA_ANGULAR18,

tempSample=((32−iFact)*p[−1][iIdx−1]+iFact*p[−1][iIdx]+16)>>5

Otherwise,

tempSample=((32−iFact)*p[iIdx−1][−1]+iFact*p[iIdx][−1]+16)>>5

refL[x][y]=p[−1][y]−tempSample+predSamples[x][y]  (429)

refT[x][y]=p[x][−1]−tempSample+predSamples[x][y]  (430)”]

wT[y]=(predModeIntra[added: “<=”]INTRA_ANGULAR18)?32>>((y<<<1)>>[added:“nScale2”]): 0  (431)

wL[x]=(predModeIntra[added: “>=”]INTRA_ANGULAR50)?32>>((x<<1)>>[added:“nScale2”]): 0  (432)

-   -   Otherwise, if predModeIntra is less than INTRA_ANGULAR18, the        following ordered steps apply:    -   1. The variables dXInt[y] and dX[x][y] are derived as follows        using invAngle as specified in clause 8.4.5.2.12 depending on        intraPredMode:

dXInt[y]=((y+1)*invAngle+256)>>9   (433)

dX[x][y]=x+dXInt[y]

-   -   2. The variables refL[x][y], refT[x][y], wT[y], and wL[x] are        derived as follows:

refL[x][y]=0  (434)

refT[x][y]=(y<(3<<nScale))?mainRef[dX[x][y]]:0  (435)

wT[y]=32>>((y<<1)>>nScale)   (436)

wL[x]=0  (437)

-   -   Otherwise, if predModeIntra is greater than INTRA_ANGULAR50, the        following ordered steps apply:    -   1. The variables dYInt[x] and dY[x][y] are derived as follows        using invAngle as specified in clause 8.4.5.2.12 depending on        intraPredMode:

dYInt[x]=((x+1)*invAngle+256)>>9   (8-243)

dY[x][y]=y+dYInt[x]

-   -   2. The variables refL[x][y], refT[x][y], wT[y], and wL[x] are        derived as follows:

refL[x][y]=(x<(3<<nScale))?sideRef[dY[x][y]]: 0  (439)

refT[x][y]=0  (440)

wT[y]=0  (441)

wL[x]=32>>((x<<1)>>nScale)   (442)

-   -   Otherwise, refL[x][y], refT[x][y], wT[y], and wL[x] are all set        equal to 0.    -   The values of the modified predicted samples predSamples[x][y],        with x=0 . . . nTbW−1, y=0 . . . nTbH−1 are derived as follows:

predSamples[x][y]=Clip1((refL[x][y]*wL[x]+refT[x][y]*wT[y]+(443)(64−wL[x]−wT[y])*predSamples[x][y]+32)>>6).

In some examples, video encoder 200 and video decoder 300 may applygradient PDPC as discussed above to only near-horizontal andnear-vertical modes, e.g., for modes 18−k1 and 50+k2, where 0<k1<=TH1,and 0<k2<=TH2. The threshold values (TH1, TH2) can be fixed or dependenton block size, quantization parameter, and/or other block parameters.TH1 and TH2 can also be specified at a picture level (e.g., in pictureheader or a picture parameter set (PPS)) or a sequence level parameter(e.g., in a sequence parameter set (SPS)). That is, video encoder 200may encode data representing TH1 and TH2 in, e.g., a VPS, SPS, PPS,picture header, slice header, block header, or the like, and videodecoder 300 may decode the data to determine TH1 and TH2, and likewise,k1 and k2.

Video encoder 200 and video decoder 300 may be configured to code a flag(e.g., a sequence level flag in an SPS or a picture level flag in a PPS)to enable/disable gradient PDPC. For example, video encoder 200 mayperform rate-distortion optimization (RDO) to determine whether gradientPDPC reduces distortion without overly increasing bitrate, and if so,may enable gradient PDPC. Additionally or alternatively, video encoder200 may enable gradient PDPC only for certain profiles, tiers, and/orlevels of a relevant video coding standard.

In some examples, video encoder 200 and video decoder 300 may applygradient PDPC to blocks where nScale<nScale2, or to blocks wheregradient PDPC will be applied in more areas compared to original PDPC.

In some examples, when nScale<nScale2, video encoder 200 and videodecoder 300 may apply original PDPC for (x<(3<<nScale)) and gradientPDPC for ((3<<nScale)<=x<((3<<nScale2)), for Case 1. Similarly, for Case2, video encoder 200 and video decoder 300 may apply original PDPC for(y<(3<<nScale)) and gradient PDPC for ((3<<nScale)<=y<((3<<nScale2)). Inthese examples, a motivation is to use “gradient PDPC” for the rows orcolumns, where original PDPC cannot be applied.

In some examples, video encoder 200 and video decoder 300 may combinethe results of conventional PDPC and gradient PDPC, e.g., in a weightedmanner, where both conventional PDPC and gradient PDPC can be applied.

In some examples, video encoder 200 and video decoder 300 may applygradient PDPC for angular modes to luma components, but not to chromacomponents.

In some examples, gradient PDPC may be disabled (or not applied) forangular modes for narrow chroma blocks (e.g., chroma blocks of N×2 or2×N). For example, video encoder 200 and video decoder 300 may determinethat a chroma block is narrow (e.g., N×2 or 2×N) and based on thedetermination that the chroma block is narrow, not apply gradient PDPCfor angular modes to that narrow block.

Video encoder 200 and video decoder 300 may apply any or all of thetechniques discussed above alone or in any combination.

FIG. 8 is a block diagram illustrating an example video encoder 200 thatmay perform the techniques of this disclosure. FIG. 8 is provided forpurposes of explanation and should not be considered limiting of thetechniques as broadly exemplified and described in this disclosure. Forpurposes of explanation, this disclosure describes video encoder 200 inthe context of video coding standards such as the HEVC video codingstandard and the H.266 video coding standard in development. However,the techniques of this disclosure are not limited to these video codingstandards, and are applicable generally to video encoding and decoding.

In the example of FIG. 8 , video encoder 200 includes video data memory230, mode selection unit 202, residual generation unit 204, transformprocessing unit 206, quantization unit 208, inverse quantization unit210, inverse transform processing unit 212, reconstruction unit 214,filter unit 216, decoded picture buffer (DPB) 218, and entropy encodingunit 220. Any or all of video data memory 230, mode selection unit 202,residual generation unit 204, transform processing unit 206,quantization unit 208, inverse quantization unit 210, inverse transformprocessing unit 212, reconstruction unit 214, filter unit 216, DPB 218,and entropy encoding unit 220 may be implemented in one or moreprocessors or in processing circuitry. Moreover, video encoder 200 mayinclude additional or alternative processors or processing circuitry toperform these and other functions.

Video data memory 230 may store video data to be encoded by thecomponents of video encoder 200. Video encoder 200 may receive the videodata stored in video data memory 230 from, for example, video source 104(FIG. 5 ). DPB 218 may act as a reference picture memory that storesreference video data for use in prediction of subsequent video data byvideo encoder 200. Video data memory 230 and DPB 218 may be formed byany of a variety of memory devices, such as dynamic random access memory(DRAM), including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM),resistive RAM (RRAM), or other types of memory devices. Video datamemory 230 and DPB 218 may be provided by the same memory device orseparate memory devices. In various examples, video data memory 230 maybe on-chip with other components of video encoder 200, as illustrated,or off-chip relative to those components.

In this disclosure, reference to video data memory 230 should not beinterpreted as being limited to memory internal to video encoder 200,unless specifically described as such, or memory external to videoencoder 200, unless specifically described as such. Rather, reference tovideo data memory 230 should be understood as reference memory thatstores video data that video encoder 200 receives for encoding (e.g.,video data for a current block that is to be encoded). Memory 106 ofFIG. 5 may also provide temporary storage of outputs from the variousunits of video encoder 200.

The various units of FIG. 8 are illustrated to assist with understandingthe operations performed by video encoder 200. The units may beimplemented as fixed-function circuits, programmable circuits, or acombination thereof. Fixed-function circuits refer to circuits thatprovide particular functionality, and are preset on the operations thatcan be performed. Programmable circuits refer to circuits that can beprogrammed to perform various tasks, and provide flexible functionalityin the operations that can be performed. For instance, programmablecircuits may execute software or firmware that cause the programmablecircuits to operate in the manner defined by instructions of thesoftware or firmware. Fixed-function circuits may execute softwareinstructions (e.g., to receive parameters or output parameters), but thetypes of operations that the fixed-function circuits perform aregenerally immutable. In some examples, one or more of the units may bedistinct circuit blocks (fixed-function or programmable), and in someexamples, the one or more units may be integrated circuits.

Video encoder 200 may include arithmetic logic units (ALUs), elementaryfunction units (EFUs), digital circuits, analog circuits, and/orprogrammable cores, formed from programmable circuits. In examples wherethe operations of video encoder 200 are performed using softwareexecuted by the programmable circuits, memory 106 (FIG. 5 ) may storethe object code of the software that video encoder 200 receives andexecutes, or another memory within video encoder 200 (not shown) maystore such instructions.

Video data memory 230 is configured to store received video data. Videoencoder 200 may retrieve a picture of the video data from video datamemory 230 and provide the video data to residual generation unit 204and mode selection unit 202. Video data in video data memory 230 may beraw video data that is to be encoded.

Mode selection unit 202 includes a motion estimation unit 222, motioncompensation unit 224, and an intra-prediction unit 226. Mode selectionunit 202 may include additional functional units to perform videoprediction in accordance with other prediction modes. As examples, modeselection unit 202 may include a palette unit, an intra-block copy unit(which may be part of motion estimation unit 222 and/or motioncompensation unit 224), an affine unit, a linear model (LM) unit, or thelike.

Mode selection unit 202 generally coordinates multiple encoding passesto test combinations of encoding parameters and resultingrate-distortion values for such combinations. The encoding parametersmay include partitioning of CTUs into CUs, prediction modes for the CUs,transform types for residual data of the CUs, quantization parametersfor residual data of the CUs, and so on. Mode selection unit 202 mayultimately select the combination of encoding parameters havingrate-distortion values that are better than the other testedcombinations.

Video encoder 200 may partition a picture retrieved from video datamemory 230 into a series of CTUs, and encapsulate one or more CTUswithin a slice. Mode selection unit 202 may partition a CTU of thepicture in accordance with a tree structure, such as the QTBT structureor the quad-tree structure of HEVC described above. As described above,video encoder 200 may form one or more CUs from partitioning a CTUaccording to the tree structure. Such a CU may also be referred togenerally as a “video block” or “block.”

In general, mode selection unit 202 also controls the components thereof(e.g., motion estimation unit 222, motion compensation unit 224, andintra-prediction unit 226) to generate a prediction block for a currentblock (e.g., a current CU, or in HEVC, the overlapping portion of a PUand a TU). For inter-prediction of a current block, motion estimationunit 222 may perform a motion search to identify one or more closelymatching reference blocks in one or more reference pictures (e.g., oneor more previously coded pictures stored in DPB 218). In particular,motion estimation unit 222 may calculate a value representative of howsimilar a potential reference block is to the current block, e.g.,according to sum of absolute difference (SAD), sum of squareddifferences (SSD), mean absolute difference (MAD), mean squareddifferences (MSD), or the like. Motion estimation unit 222 may generallyperform these calculations using sample-by-sample differences betweenthe current block and the reference block being considered. Motionestimation unit 222 may identify a reference block having a lowest valueresulting from these calculations, indicating a reference block thatmost closely matches the current block.

Motion estimation unit 222 may form one or more motion vectors (MVs)that defines the positions of the reference blocks in the referencepictures relative to the position of the current block in a currentpicture. Motion estimation unit 222 may then provide the motion vectorsto motion compensation unit 224. For example, for uni-directionalinter-prediction, motion estimation unit 222 may provide a single motionvector, whereas for bi-directional inter-prediction, motion estimationunit 222 may provide two motion vectors. Motion compensation unit 224may then generate a prediction block using the motion vectors. Forexample, motion compensation unit 224 may retrieve data of the referenceblock using the motion vector. As another example, if the motion vectorhas fractional sample precision, motion compensation unit 224 mayinterpolate values for the prediction block according to one or moreinterpolation filters. Moreover, for bi-directional inter-prediction,motion compensation unit 224 may retrieve data for two reference blocksidentified by respective motion vectors and combine the retrieved data,e.g., through sample-by-sample averaging or weighted averaging.

As another example, for intra-prediction, or intra-prediction coding,intra-prediction unit 226 may generate the prediction block from samplesneighboring the current block. For example, for directional modes,intra-prediction unit 226 may generally mathematically combine values ofneighboring samples and populate these calculated values in the defineddirection across the current block to produce the prediction block. Asanother example, for DC mode, intra-prediction unit 226 may calculate anaverage of the neighboring samples to the current block and generate theprediction block to include this resulting average for each sample ofthe prediction block.

Intra-prediction unit 226 may also perform the gradient PDPC techniquesof this disclosure. Intra-prediction unit 226 may initially form aprediction block for a current block using an angular intra-predictionmode. Intra-prediction unit 226 may also determine that the angularintra-prediction mode is a mode between 50 and 81 or less than 18 otherthan 1 and 0. In response, intra-prediction unit 226 may performgradient PDPC.

In particular, as discussed above, intra-prediction unit 226 maydetermine a prediction direction of the angular intra-prediction mode.Intra-prediction unit 226 may calculate a gradient term for a sample ofthe current block along the prediction direction. For example,intra-prediction unit 226 may calculate an intensity variation along theprediction direction, as discussed above, e.g., with respect to FIG. 6 .Intra-prediction unit 226 may then combine the gradient term with thepredicted value of the sample to form a final value for the sample.Intra-prediction unit 226 may perform these techniques for multiplesamples (e.g., all samples or fewer than all samples) of the predictionblock.

In some examples, when combining the gradient term with the predictedvalue, intra-prediction unit 226 may weight the gradient term and thepredicted value, e.g., using weights having a combined sum of 1.Intra-prediction unit 226 may determine the weights based on, e.g., adistance between a position of a sample and a corresponding primaryboundary (i.e., a boundary from which the predicted value wascalculated). For example, when the intra-prediction mode is anupper-right angular intra-prediction mode, intra-prediction unit 226 maydetermine a weight to apply to the intra-predicted sample according to adistance between a position of the sample and a horizontally neighboringreference sample. As another example, when the intra-prediction mode isa lower-left angular intra-prediction mode, intra-prediction unit 226may determine a weight to apply to the intra-predicted sample accordingto a distance between the position of the sample and a verticallyneighboring reference sample.

In some examples, intra-prediction unit 226 may determine whether toapply gradient PDPC to the current block based on other factors beyondthe angular intra-prediction direction used. For example, mode selectionunit 202 may execute multiple encoding passes, comparing use of gradientPDPC to not using gradient PDPC for one or more blocks (e.g., multipleblocks in a slice, multiple slices, multiple pictures, etc.) Modeselection unit 202 may calculate rate-distortion optimization (RDO)values for each encoding pass and determine whether or not to enablegradient PDPC based on whether the RDO values when gradient PDPC isenabled are better than the RDO values when gradient PDPC is disabled.

In some examples (in addition or in the alternative to the above),intra-prediction unit 226 may calculate an nScale value and an nScale2value for the current block as discussed above, and use these values todetermine whether or not to apply gradient PDPC. For example,intra-prediction unit 226 may be configured to apply gradient PDPC toall blocks for which nScale2 is greater than or equal to zero. Asanother example, intra-prediction unit 226 may determine to applygradient PDPC when nScale is less than nScale2. Additionally oralternatively, intra-prediction unit 226 may be configured to applygradient PDPC only to luminance (luma) blocks, and not to chroma blocks.Additionally or alternatively, intra-prediction unit 226 may beconfigured to apply gradient PDPC only to blocks larger than 4×4.

In some examples, mode selection unit 202 may further encode explicitdata representing whether gradient PDPC is enabled. For example, modeselection unit 202 may form a VPS, SPS, PPS, picture header, sliceheader, block header, or the like including data indicating whethergradient PDPC is enabled. Mode selection unit 202 may provide this datastructure to entropy encoding unit 220 to be encoded as part of thebitstream.

Mode selection unit 202 provides the prediction block to residualgeneration unit 204. Residual generation unit 204 receives a raw,uncoded version of the current block from video data memory 230 and theprediction block from mode selection unit 202. Residual generation unit204 calculates sample-by-sample differences between the current blockand the prediction block. The resulting sample-by-sample differencesdefine a residual block for the current block. In some examples,residual generation unit 204 may also determine differences betweensample values in the residual block to generate a residual block usingresidual differential pulse code modulation (RDPCM). In some examples,residual generation unit 204 may be formed using one or more subtractorcircuits that perform binary subtraction.

In examples where mode selection unit 202 partitions CUs into PUs, eachPU may be associated with a luma prediction unit and correspondingchroma prediction units. Video encoder 200 and video decoder 300 maysupport PUs having various sizes. As indicated above, the size of a CUmay refer to the size of the luma coding block of the CU and the size ofa PU may refer to the size of a luma prediction unit of the PU. Assumingthat the size of a particular CU is 2N×2N, video encoder 200 may supportPU sizes of 2N×2N or N×N for intra-prediction, and symmetric PU sizes of2N×2N, 2N×N, N×2N, N×N, or similar for inter prediction. Video encoder200 and video decoder 300 may also support asymmetric partitioning forPU sizes of 2N×nU, 2N×nD, nL×2N, and nR×2N for inter prediction.

In examples where mode selection unit 202 does not further partition aCU into PUs, each CU may be associated with a luma coding block andcorresponding chroma coding blocks. As above, the size of a CU may referto the size of the luma coding block of the CU. The video encoder 200and video decoder 300 may support CU sizes of 2N×2N, 2N×N, or N×2N.

For other video coding techniques such as intra-block copy mode coding,affine-mode coding, and linear model (LM) mode coding, as some examples,mode selection unit 202, via respective units associated with the codingtechniques, generates a prediction block for the current block beingencoded. In some examples, such as palette mode coding, mode selectionunit 202 may not generate a prediction block, and instead generatessyntax elements that indicate the manner in which to reconstruct theblock based on a selected palette. In such modes, mode selection unit202 may provide these syntax elements to entropy encoding unit 220 to beencoded.

As described above, residual generation unit 204 receives the video datafor the current block and the corresponding prediction block. Residualgeneration unit 204 then generates a residual block for the currentblock. To generate the residual block, residual generation unit 204calculates sample-by-sample differences between the prediction block andthe current block.

Transform processing unit 206 applies one or more transforms to theresidual block to generate a block of transform coefficients (referredto herein as a “transform coefficient block”). Transform processing unit206 may apply various transforms to a residual block to form thetransform coefficient block. For example, transform processing unit 206may apply a discrete cosine transform (DCT), a directional transform, aKarhunen-Loeve transform (KLT), or a conceptually similar transform to aresidual block. In some examples, transform processing unit 206 mayperform multiple transforms to a residual block, e.g., a primarytransform and a secondary transform, such as a rotational transform. Insome examples, transform processing unit 206 does not apply transformsto a residual block.

Quantization unit 208 may quantize the transform coefficients in atransform coefficient block, to produce a quantized transformcoefficient block. Quantization unit 208 may quantize transformcoefficients of a transform coefficient block according to aquantization parameter (QP) value associated with the current block.Video encoder 200 (e.g., via mode selection unit 202) may adjust thedegree of quantization applied to the transform coefficient blocksassociated with the current block by adjusting the QP value associatedwith the CU. Quantization may introduce loss of information, and thus,quantized transform coefficients may have lower precision than theoriginal transform coefficients produced by transform processing unit206.

Inverse quantization unit 210 and inverse transform processing unit 212may apply inverse quantization and inverse transforms to a quantizedtransform coefficient block, respectively, to reconstruct a residualblock from the transform coefficient block. Reconstruction unit 214 mayproduce a reconstructed block corresponding to the current block (albeitpotentially with some degree of distortion) based on the reconstructedresidual block and a prediction block generated by mode selection unit202. For example, reconstruction unit 214 may add samples of thereconstructed residual block to corresponding samples from theprediction block generated by mode selection unit 202 to produce thereconstructed block.

Filter unit 216 may perform one or more filter operations onreconstructed blocks. For example, filter unit 216 may performdeblocking operations to reduce blockiness artifacts along edges of CUs.Operations of filter unit 216 may be skipped, in some examples.

Video encoder 200 stores reconstructed blocks in DPB 218. For instance,in examples where operations of filter unit 216 are not needed,reconstruction unit 214 may store reconstructed blocks to DPB 218. Inexamples where operations of filter unit 216 are needed, filter unit 216may store the filtered reconstructed blocks to DPB 218. Motionestimation unit 222 and motion compensation unit 224 may retrieve areference picture from DPB 218, formed from the reconstructed (andpotentially filtered) blocks, to inter-predict blocks of subsequentlyencoded pictures. In addition, intra-prediction unit 226 may usereconstructed blocks in DPB 218 of a current picture to intra-predictother blocks in the current picture.

In general, entropy encoding unit 220 may entropy encode syntax elementsreceived from other functional components of video encoder 200. Forexample, entropy encoding unit 220 may entropy encode quantizedtransform coefficient blocks from quantization unit 208. As anotherexample, entropy encoding unit 220 may entropy encode prediction syntaxelements (e.g., motion information for inter-prediction or intra-modeinformation for intra-prediction) from mode selection unit 202. Entropyencoding unit 220 may perform one or more entropy encoding operations onthe syntax elements, which are another example of video data, togenerate entropy-encoded data. For example, entropy encoding unit 220may perform a context-adaptive variable length coding (CAVLC) operation,a CABAC operation, a variable-to-variable (V2V) length coding operation,a syntax-based context-adaptive binary arithmetic coding (SBAC)operation, a Probability Interval Partitioning Entropy (PIPE) codingoperation, an Exponential-Golomb encoding operation, or another type ofentropy encoding operation on the data. In some examples, entropyencoding unit 220 may operate in bypass mode where syntax elements arenot entropy encoded.

Video encoder 200 may output a bitstream that includes the entropyencoded syntax elements needed to reconstruct blocks of a slice orpicture. In particular, entropy encoding unit 220 may output thebitstream.

The operations described above are described with respect to a block.Such description should be understood as being operations for a lumacoding block and/or chroma coding blocks. As described above, in someexamples, the luma coding block and chroma coding blocks are luma andchroma components of a CU. In some examples, the luma coding block andthe chroma coding blocks are luma and chroma components of a PU.

In some examples, operations performed with respect to a luma codingblock need not be repeated for the chroma coding blocks. As one example,operations to identify a motion vector (MV) and reference picture for aluma coding block need not be repeated for identifying a MV andreference picture for the chroma blocks. Rather, the MV for the lumacoding block may be scaled to determine the MV for the chroma blocks,and the reference picture may be the same. As another example, theintra-prediction process may be the same for the luma coding block andthe chroma coding blocks.

Video encoder 200 represents an example of a device for encoding anddecoding video data including a memory configured to store video data;and one or more processors implemented in circuitry and configured to:generate an intra-prediction block for a current block of video datausing an angular intra-prediction mode, the angular intra-predictionmode being an upper-right angular intra-prediction mode or a lower-leftangular intra-prediction mode; determine a prediction direction of theangular intra-prediction mode; for at least one sample of the predictionblock for the current block: calculate a gradient term for the samplealong the prediction direction; and combine a value of anintra-predicted sample of the intra-prediction block at a position ofthe sample of the prediction block with the gradient term to produce avalue of the sample of the prediction block; and decode the currentblock using the prediction block.

FIG. 9 is a block diagram illustrating an example video decoder 300 thatmay perform the techniques of this disclosure. FIG. 9 is provided forpurposes of explanation and is not limiting on the techniques as broadlyexemplified and described in this disclosure. For purposes ofexplanation, this disclosure describes video decoder 300 according tothe techniques of JEM, VVC, and HEVC. However, the techniques of thisdisclosure may be performed by video coding devices that are configuredto other video coding standards.

In the example of FIG. 9 , video decoder 300 includes coded picturebuffer (CPB) memory 320, entropy decoding unit 302, predictionprocessing unit 304, inverse quantization unit 306, inverse transformprocessing unit 308, reconstruction unit 310, filter unit 312, anddecoded picture buffer (DPB) 314. Any or all of CPB memory 320, entropydecoding unit 302, prediction processing unit 304, inverse quantizationunit 306, inverse transform processing unit 308, reconstruction unit310, filter unit 312, and DPB 314 may be implemented in one or moreprocessors or in processing circuitry. Moreover, video decoder 300 mayinclude additional or alternative processors or processing circuitry toperform these and other functions.

Prediction processing unit 304 includes motion compensation unit 316 andintra-prediction unit 318. Prediction processing unit 304 may includeadditional units to perform prediction in accordance with otherprediction modes. As examples, prediction processing unit 304 mayinclude a palette unit, an intra-block copy unit (which may form part ofmotion compensation unit 316), an affine unit, a linear model (LM) unit,or the like. In other examples, video decoder 300 may include more,fewer, or different functional components.

CPB memory 320 may store video data, such as an encoded video bitstream,to be decoded by the components of video decoder 300. The video datastored in CPB memory 320 may be obtained, for example, fromcomputer-readable medium 110 (FIG. 5 ). CPB memory 320 may include a CPBthat stores encoded video data (e.g., syntax elements) from an encodedvideo bitstream. Also, CPB memory 320 may store video data other thansyntax elements of a coded picture, such as temporary data representingoutputs from the various units of video decoder 300. DPB 314 generallystores decoded pictures, which video decoder 300 may output and/or useas reference video data when decoding subsequent data or pictures of theencoded video bitstream. CPB memory 320 and DPB 314 may be formed by anyof a variety of memory devices, such as dynamic random access memory(DRAM), including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM),resistive RAM (RRAM), or other types of memory devices. CPB memory 320and DPB 314 may be provided by the same memory device or separate memorydevices. In various examples, CPB memory 320 may be on-chip with othercomponents of video decoder 300, or off-chip relative to thosecomponents.

Additionally or alternatively, in some examples, video decoder 300 mayretrieve coded video data from memory 120 (FIG. 5 ). That is, memory 120may store data as discussed above with CPB memory 320. Likewise, memory120 may store instructions to be executed by video decoder 300, whensome or all of the functionality of video decoder 300 is implemented insoftware to be executed by processing circuitry of video decoder 300.

The various units shown in FIG. 9 are illustrated to assist withunderstanding the operations performed by video decoder 300. The unitsmay be implemented as fixed-function circuits, programmable circuits, ora combination thereof. Similar to FIG. 8 , fixed-function circuits referto circuits that provide particular functionality, and are preset on theoperations that can be performed. Programmable circuits refer tocircuits that can be programmed to perform various tasks, and provideflexible functionality in the operations that can be performed. Forinstance, programmable circuits may execute software or firmware thatcause the programmable circuits to operate in the manner defined byinstructions of the software or firmware. Fixed-function circuits mayexecute software instructions (e.g., to receive parameters or outputparameters), but the types of operations that the fixed-functioncircuits perform are generally immutable. In some examples, the one ormore units may be distinct circuit blocks (fixed-function orprogrammable), and in some examples, the one or more units may beintegrated circuits.

Video decoder 300 may include ALUs, EFUs, digital circuits, analogcircuits, and/or programmable cores formed from programmable circuits.In examples where the operations of video decoder 300 are performed bysoftware executing on the programmable circuits, on-chip or off-chipmemory may store instructions (e.g., object code) of the software thatvideo decoder 300 receives and executes.

Entropy decoding unit 302 may receive encoded video data from the CPBand entropy decode the video data to reproduce syntax elements.Prediction processing unit 304, inverse quantization unit 306, inversetransform processing unit 308, reconstruction unit 310, and filter unit312 may generate decoded video data based on the syntax elementsextracted from the bitstream.

In general, video decoder 300 reconstructs a picture on a block-by-blockbasis. Video decoder 300 may perform a reconstruction operation on eachblock individually (where the block currently being reconstructed, i.e.,decoded, may be referred to as a “current block”).

Entropy decoding unit 302 may entropy decode syntax elements definingquantized transform coefficients of a quantized transform coefficientblock, as well as transform information, such as a quantizationparameter (QP) and/or transform mode indication(s). Inverse quantizationunit 306 may use the QP associated with the quantized transformcoefficient block to determine a degree of quantization and, likewise, adegree of inverse quantization for inverse quantization unit 306 toapply. Inverse quantization unit 306 may, for example, perform a bitwiseleft-shift operation to inverse quantize the quantized transformcoefficients. Inverse quantization unit 306 may thereby form a transformcoefficient block including transform coefficients.

After inverse quantization unit 306 forms the transform coefficientblock, inverse transform processing unit 308 may apply one or moreinverse transforms to the transform coefficient block to generate aresidual block associated with the current block. For example, inversetransform processing unit 308 may apply an inverse DCT, an inverseinteger transform, an inverse Karhunen-Loeve transform (KLT), an inverserotational transform, an inverse directional transform, or anotherinverse transform to the transform coefficient block.

Furthermore, prediction processing unit 304 generates a prediction blockaccording to prediction information syntax elements that were entropydecoded by entropy decoding unit 302. For example, if the predictioninformation syntax elements indicate that the current block isinter-predicted, motion compensation unit 316 may generate theprediction block. In this case, the prediction information syntaxelements may indicate a reference picture in DPB 314 from which toretrieve a reference block, as well as a motion vector identifying alocation of the reference block in the reference picture relative to thelocation of the current block in the current picture. Motioncompensation unit 316 may generally perform the inter-prediction processin a manner that is substantially similar to that described with respectto motion compensation unit 224 (FIG. 8 ).

As another example, if the prediction information syntax elementsindicate that the current block is intra-predicted, intra-predictionunit 318 may generate the prediction block according to anintra-prediction mode indicated by the prediction information syntaxelements. Again, intra-prediction unit 318 may generally perform theintra-prediction process in a manner that is substantially similar tothat described with respect to intra-prediction unit 226 (FIG. 8 ).Intra-prediction unit 318 may perform the gradient PDPC techniques ofthis disclosure. Intra-prediction unit 318 may retrieve data ofneighboring samples to the current block from DPB 314.

In some examples, entropy decoding unit 302 may decode explicit datarepresenting whether gradient PDPC is enabled. For example, entropydecoding unit 302 may decode a VPS, SPS, PPS, picture header, sliceheader, block header, or the like including data indicating whethergradient PDPC is enabled. Entropy decoding unit 302 may provide thedecoded data to intra-prediction unit 318 indicating whether gradientPDPC is enabled for a particular sequence of pictures, picture, slice,block, or the like.

Intra-prediction unit 318 may perform the gradient PDPC techniques ofthis disclosure. Intra-prediction unit 318 may initially form aprediction block for a current block using an angular intra-predictionmode. Intra-prediction unit 318 may also determine that the angularintra-prediction mode is a mode between 50 and 81 or less than 18 otherthan 1 and 0. In response, intra-prediction unit 318 may performgradient PDPC.

In particular, as discussed above, intra-prediction unit 318 maydetermine a prediction direction of the angular intra-prediction mode.Intra-prediction unit 318 may calculate a gradient term for a sample ofthe current block along the prediction direction. For example,intra-prediction unit 318 may calculate an intensity variation along theprediction direction, as discussed above, e.g., with respect to FIG. 6 .Intra-prediction unit 318 may then combine the gradient term with thepredicted value of the sample to form a final value for the sample.Intra-prediction unit 318 may perform these techniques for multiplesamples (e.g., all samples or fewer than all samples) of the predictionblock.

In some examples, when combining the gradient term with the predictedvalue, intra-prediction unit 318 may weight the gradient term and thepredicted value, e.g., using weights having a combined sum of 1.Intra-prediction unit 318 may determine the weights based on, e.g., adistance between a position of a sample and a corresponding primaryboundary (i.e., a boundary from which the predicted value wascalculated). For example, when the intra-prediction mode is anupper-right angular intra-prediction mode, intra-prediction unit 318 maydetermine a weight to apply to the intra-predicted sample according to adistance between a position of the sample and a horizontally neighboringreference sample. As another example, when the intra-prediction mode isa lower-left angular intra-prediction mode, intra-prediction unit 318may determine a weight to apply to the intra-predicted sample accordingto a distance between the position of the sample and a verticallyneighboring reference sample.

In some examples, intra-prediction unit 318 may determine whether toapply gradient PDPC to the current block based on other factors beyondthe angular intra-prediction direction used. As discussed above,intra-prediction unit 318 may receive data from entropy decoding unit302 indicating whether gradient PDPC is enabled.

In some examples (in addition or in the alternative to the above),intra-prediction unit 318 may calculate an nScale value and an nScale2value for the current block as discussed above, and use these values todetermine whether or not to apply gradient PDPC. For example,intra-prediction unit 318 may be configured to apply gradient PDPC toall blocks for which nScale2 is greater than or equal to zero. Asanother example, intra-prediction unit 318 may determine to applygradient PDPC when nScale is less than nScale2. Additionally oralternatively, intra-prediction unit 318 may be configured to applygradient PDPC only to luminance (luma) blocks, and not to chroma blocks.Additionally or alternatively, intra-prediction unit 318 may beconfigured to apply gradient PDPC only to blocks larger than 4×4.

Reconstruction unit 310 may reconstruct the current block using theprediction block and the residual block. For example, reconstructionunit 310 may add samples of the residual block to corresponding samplesof the prediction block to reconstruct the current block.

Filter unit 312 may perform one or more filter operations onreconstructed blocks. For example, filter unit 312 may performdeblocking operations to reduce blockiness artifacts along edges of thereconstructed blocks. Operations of filter unit 312 are not necessarilyperformed in all examples.

Video decoder 300 may store the reconstructed blocks in DPB 314. Asdiscussed above, DPB 314 may provide reference information, such assamples of a current picture for intra-prediction and previously decodedpictures for subsequent motion compensation, to prediction processingunit 304. Moreover, video decoder 300 may output decoded pictures fromDPB 314 for subsequent presentation on a display device, such as displaydevice 118 of FIG. 1 .

In this manner, video decoder 300 represents an example of a device fordecoding video data that includes a memory configured to store videodata; and one or more processors implemented in circuitry and configuredto: generate an intra-prediction block for a current block of video datausing an angular intra-prediction mode, the angular intra-predictionmode being an upper-right angular intra-prediction mode or a lower-leftangular intra-prediction mode; determine a prediction direction of theangular intra-prediction mode; for at least one sample of the predictionblock for the current block: calculate a gradient term for the samplealong the prediction direction; and combine a value of anintra-predicted sample of the intra-prediction block at a position ofthe sample of the prediction block with the gradient term to produce avalue of the sample of the prediction block; and decode the currentblock using the prediction block.

FIG. 10 is a flowchart illustrating an example method for encoding acurrent block in accordance with the techniques of this disclosure. Thecurrent block may comprise a current CU. Although described with respectto video encoder 200 (FIGS. 5 and 8 ), it should be understood thatother devices may be configured to perform a method similar to that ofFIG. 10 .

In this example, video encoder 200 initially predicts the current block(350). For example, video encoder 200 may form a prediction block forthe current block. In particular, video encoder 200 may form theprediction block using the gradient PDPC techniques of this disclosure.For example, video encoder 200 may determine a direction for an angularintra-prediction mode for the current block. Video encoder 200 may then,for at least one sample (but potentially multiple or all samples) of thecurrent block, calculate gradient term(s) along the prediction directionand combine predicted values with the corresponding gradient terms toultimately form the final prediction block for the current block.

Video encoder 200 may then calculate a residual block for the currentblock (352). To calculate the residual block, video encoder 200 maycalculate a difference between the original, uncoded block and theprediction block for the current block. Video encoder 200 may thentransform and quantize coefficients of the residual block (354). Next,video encoder 200 may scan the quantized transform coefficients of theresidual block (356). During the scan, or following the scan, videoencoder 200 may entropy encode the coefficients (358). For example,video encoder 200 may encode the coefficients using CAVLC or CABAC.Video encoder 200 may then output the entropy coded data of the block(360).

After encoding the current block, video encoder 200 may also decode thecurrent block. As discussed above, video encoder 200 includes videodecoding components, sometimes referred to as a decoding loop. Thesedecoding components include inverse quantization unit 210, inversetransform processing unit 212, reconstruction unit 214, filter unit 216,and DPB 218 (FIG. 8 ). Thus, after encoding the current block, inversequantization unit 210 and inverse transform processing unit 212 mayinverse quantize and inverse transform the quantized transformcoefficients to reproduce the residual block (362). Reconstruction unit214 may then combine the residual block and the prediction block (on asample-by-sample basis) to decode the current block (364). Video encoder200 may then store the decoded block in DPB 218 (366). In some examples,filter unit 216 may filter the decoded block prior to storage in DPB218. In this manner, video encoder 200 may both encode and decode thecurrent block, such that reference blocks stored in DPB 218 are the sameas decoded reference blocks reconstructed by a video decoder, such asvideo decoder 300.

In this manner, the method of FIG. 10 represents an example of a methodof encoding and decoding video data including generating anintra-prediction block for a current block of video data using anangular intra-prediction mode, the angular intra-prediction mode beingan upper-right angular intra-prediction mode or a lower-left angularintra-prediction mode; determining a prediction direction of the angularintra-prediction mode; for at least one sample of the prediction blockfor the current block: calculating a gradient term for the sample alongthe prediction direction; and combining a value of an intra-predictedsample of the intra-prediction block at a position of the sample of theprediction block with the gradient term to produce a value of the sampleof the prediction block; and decoding the current block using theprediction block.

FIG. 11 is a flowchart illustrating an example method for decoding acurrent block in accordance with the techniques of this disclosure. Thecurrent block may comprise a current CU. Although described with respectto video decoder 300 (FIGS. 5 and 9 ), it should be understood thatother devices may be configured to perform a method similar to that ofFIG. 11 .

Video decoder 300 may receive entropy coded data for the current block,such as entropy coded prediction information and entropy coded data forcoefficients of a residual block corresponding to the current block(370). Video decoder 300 may entropy decode the entropy coded data todetermine prediction information for the current block and to reproducecoefficients of the residual block (372). Video decoder 300 may predictthe current block (374), e.g., using an intra- or inter-prediction modeas indicated by the prediction information for the current block, tocalculate a prediction block for the current block.

Video decoder 300 may form the prediction block using the gradient PDPCtechniques of this disclosure. In particular, video decoder 300 may formthe prediction block using the gradient PDPC techniques of thisdisclosure. For example, video decoder 300 may determine a direction foran angular intra-prediction mode for the current block. Video decoder300 may then, for at least one sample (but potentially multiple or allsamples) of the current block, calculate gradient term(s) along theprediction direction and combine predicted values with the correspondinggradient terms to ultimately form the final prediction block for thecurrent block.

Video decoder 300 may then inverse scan the reproduced coefficients(376), to create a block of quantized transform coefficients. Videodecoder 300 may then inverse quantize and inverse transform thecoefficients to produce a residual block (378). Video decoder 300 mayultimately decode the current block by combining the prediction blockand the residual block (380).

In this manner, the method of FIG. 11 represents an example of a methodof decoding video data including generating an intra-prediction blockfor a current block of video data using an angular intra-predictionmode, the angular intra-prediction mode being an upper-right angularintra-prediction mode or a lower-left angular intra-prediction mode;determining a prediction direction of the angular intra-prediction mode;for at least one sample of the prediction block for the current block:calculating a gradient term for the sample along the predictiondirection; and combining a value of an intra-predicted sample of theintra-prediction block at a position of the sample of the predictionblock with the gradient term to produce a value of the sample of theprediction block; and decoding the current block using the predictionblock.

FIG. 12 is a flowchart illustrating an example method of predicting ablock using gradient PDPC according to the techniques of thisdisclosure. For purposes of example and explanation, the method of FIG.12 is explained with respect to video decoder 300 (FIGS. 5 and 9 ).However, it should be understood that other devices may perform this ora similar method, such as video encoder 200 of FIGS. 5 and 8 . Videoencoder 200 may perform the method of FIG. 12 as part of step 350 of themethod of FIG. 10 , while video decoder 300 may perform the method ofFIG. 12 as part of step 374 of FIG. 11 .

Video decoder 300 may initially determine that gradient PDPC is enabled(400). For example, video decoder 300 may decode syntax data, such as aVPS, SPS, PPS, picture header, slice header, block header, or the like,indicating that gradient PDPC is enabled for a corresponding unit ofvideo data (entire video, sequence, picture, slice, block, etc.)Additionally or alternatively, video decoder 300 may determine to usegradient PDPC for a current block according to implicit data, such as ablock size (e.g., being greater than 4×4 and/or not a thin block, suchas 2×N or N×2), whether the current block is a luma block or a chromablock, nScale and nScale2 values for the current block, or the like.

Video decoder 300 may then generate an intra-prediction block using anangular intra-prediction mode (402). The angular intra-prediction modemay particularly be an upper-right angular intra-prediction mode or alower-left angular intra-prediction mode. Upper-right angularintra-prediction modes may include modes having mode numbers greaterthan 50 and less than 81, while lower-left angular intra-predictionmodes may include modes having mode numbers less than 18 but not 0and 1. In some examples, video decoder 300 may determine that gradientPDPC is restricted to even fewer modes, e.g., using values of k1 and k2.For example, video decoder 300 may determine that upper-right angularintra-prediction modes have mode numbers greater than 50 and less than50+k2, and that lower-left angular intra-prediction modes have modenumbers less than 18−k1. Video decoder 300 may further determine k1 andk2 from syntax data, from pre-configured data, or according to a size ofthe current block and/or a quantization parameter for the current block.Video decoder 300 may then determine that gradient PDPC applies for theangular intra-prediction mode (404).

Video decoder 300 may determine a prediction direction for the angularintra-prediction mode (406). Video decoder 300 may calculate a gradientterm for a sample of the prediction block along the prediction direction(408). Video decoder 300 may then combine the predicted value of thesample with the gradient term (410) to produce a final value of thesample. Video decoder 300 may similarly update values of other samplesof the prediction block using respective gradient terms.

In this manner, the method of FIG. 12 represents an example of a methodof decoding video data, including generating an intra-prediction blockfor a current block of video data using an angular intra-predictionmode, the angular intra-prediction mode being an upper-right angularintra-prediction mode or a lower-left angular intra-prediction mode;determining a prediction direction of the angular intra-prediction mode;for at least one sample of the prediction block for the current block:calculating a gradient term for the sample along the predictiondirection; and combining a value of an intra-predicted sample of theintra-prediction block at a position of the sample of the predictionblock with the gradient term to produce a value of the sample of theprediction block; and decoding the current block using the predictionblock.

Various techniques of this disclosure are summarized in the followingclauses:

Clause 1: A method of coding video data, the method comprising:generating an intra-prediction block for a current block of video datausing an angular intra-prediction mode, the angular intra-predictionmode being an upper-right angular intra-prediction mode or a lower-leftangular intra-prediction mode; determining a prediction direction of theangular intra-prediction mode; for each sample of a prediction block ofthe current block: calculating a gradient term for the sample along theprediction direction; and combining a value of an intra-predicted sampleof the intra-prediction block at a position of the sample of theprediction block with the gradient term to produce a value of the sampleof the prediction block; and coding the current block using theprediction block.

Clause 2: The method of clause 1, wherein the angular intra-predictionmode comprises the upper-right angular intra-prediction mode having amode number greater than 50 and less than 81.

Clause 3: The method of clause 1, wherein the angular intra-predictionmode comprises the lower-left angular intra-prediction mode having amode number less than 18 and not being 0 or 1.

Clause 4: The method of any of clauses 1-3, further comprising, for eachsample, calculating a displacement value using an angle of the angularintra-prediction mode, wherein calculating the gradient term comprisescalculating the gradient term using the displacement value.

Clause 5: The method of clause 4, wherein d comprises the displacementvalue, (x,y) comprises the position of the sample, and calculating thegradient term comprises: when the angular intra-prediction mode is theupper-right angular intra-prediction mode, calculating the gradient termas being equal to r(−1,y)−r(−1+d, −1); or when the angularintra-prediction mode is the lower-left angular intra-prediction mode,calculating the gradient term as being equal to r(x, −1)−r(−1, −1+d),wherein r(x′,y′) represents a reference sample of a current pictureincluding the current block, the reference sample neighboring thecurrent block in the current picture.

Clause 6: The method of any of clauses 1-5, wherein combining comprisesapplying a first weight to the value of the intra-predicted sample and asecond weight to the gradient term.

Clause 7: The method of clause 6, further comprising: when the angularintra-prediction mode is the upper-right angular intra-prediction mode,determining the first weight according to a distance between theposition of the sample and a position of a horizontally neighboringreference sample of a current picture including the current block; orwhen the angular intra-prediction mode is the lower-left angularintra-prediction mode, determining the first weight according to adistance between the position of the sample and a position of avertically neighboring reference sample of the current picture.

Clause 8: The method of any of clauses 1-7, further comprisingdetermining that an nScale value for the current block is less thanzero.

Clause 9: The method of any of clauses 1-8, wherein the lower-leftangular intra-prediction mode comprises a near lower-left angularintra-prediction mode having a mode number less than 18 and greater than18−k1, the upper-right angular intra-prediction mode comprises a nearupper-right angular intra-prediction mode having a mode number greaterthan 50 and less than 50+k2.

Clause 10: The method of clause 9, wherein k1 and k2 are fixed values.

Clause 11: The method of clause 9, further comprising calculating k1 andk2 according to at least one of a size of the current block or aquantization parameter for the current block.

Clause 12: The method of clause 9, further comprising coding parameterset data representing k1 and k2, the parameter set data comprising dataof a sequence parameter set (SPS) or a picture parameter set (PPS).

Clause 13: The method of any of clauses 1-12, further comprising codingparameter set data enabling a gradient position-dependentintra-prediction (PDPC) mode for a current picture including the currentblock.

Clause 14: The method of any of clauses 1-13, further comprisingdetermining that an nScale value for the current block is less than annScale2 value for the current block.

Clause 15: The method of any of clauses 1-14, wherein the combining thevalue of the intra-predicted sample of the intra-prediction block at theposition of the sample of the prediction block with the gradient term toproduce the value of the sample of the prediction block is onlyperformed for a luma component of the current block.

Clause 16: The method of any of clauses 1-15, wherein the combining thevalue of the intra-predicted sample of the intra-prediction block at theposition of the sample of the prediction block with the gradient term toproduce the value of the sample of the prediction block is not performedfor a chroma component of the current block.

Clause 17: The method of any of clauses 1-16, further comprising:determining whether a chroma block of the current block is narrow; andbased on the chroma block of the current block not being narrow,combining the value of the intra-predicted sample of theintra-prediction block at the position of the sample of the predictionblock with the gradient term to produce the value of the sample of theprediction block.

Clause 18: The method of any of clauses 1-17, further comprising:determining whether a chroma block of the current block is narrow; andbased on the chroma block of the current block being narrow, notcombining the value of the intra-predicted sample of theintra-prediction block at the position of the sample of the predictionblock with the gradient term to produce the value of the sample of theprediction block.

Clause 19: The method of any of clauses 1-18, wherein coding the currentblock comprises decoding the current block, comprising: decoding aresidual block for the current block; and combining the prediction blockwith the residual block to produce a decoded version of the currentblock.

Clause 20: The method of any of clauses 1-19, wherein coding the currentblock comprises encoding the current block, comprising: calculating aresidual block representing differences between the current block andthe prediction block; and encoding the residual block.

Clause 21: A device for coding video data, the device comprising meansfor performing the method of any of clauses 1-18.

Clause 22: The device of clause 19, wherein the one or more meanscomprise one or more processors implemented in circuitry.

Clause 23: The device of clause 19, further comprising a displayconfigured to display the video data.

Clause 24: The device of clause 19, wherein the device comprises one ormore of a camera, a computer, a mobile device, a broadcast receiverdevice, or a set-top box.

Clause 25: The device of clause 17, further comprising a memoryconfigured to store the video data.

Clause 26: A device for coding video data, the device comprising: meansfor generating an intra-prediction block for a current block of videodata using an angular intra-prediction mode, the angularintra-prediction mode being an upper-right angular intra-prediction modeor a lower-left angular intra-prediction mode; means for determining aprediction direction of the angular intra-prediction mode; means forcalculating a respective gradient term for each sample of a predictionblock of the current block along the prediction direction; means forcombining a value of an intra-predicted sample of the intra-predictionblock at a position of each sample of the prediction block with therespective gradient term corresponding to the sample of the predictionblock to produce a value of the sample of the prediction block; andmeans for coding the current block using the prediction block.

Clause 27: A computer-readable storage medium having stored thereoninstructions that, when executed, cause a processor of a device forcoding video data to perform the method of any of clauses 1-16. It is tobe recognized that depending on the clause, certain acts or events ofany of the techniques described herein can be performed in a differentsequence, may be added, merged, or left out altogether (e.g., not alldescribed acts or events are necessary for the practice of thetechniques). Moreover, in certain clauses, acts or events may beperformed concurrently, e.g., through multi-threaded processing,interrupt processing, or multiple processors, rather than sequentially.

In one or more examples, the functions described may be implemented inhardware, software, firmware, or any combination thereof. If implementedin software, the functions may be stored on or transmitted over as oneor more instructions or code on a computer-readable medium and executedby a hardware-based processing unit. Computer-readable media may includecomputer-readable storage media, which corresponds to a tangible mediumsuch as data storage media, or communication media including any mediumthat facilitates transfer of a computer program from one place toanother, e.g., according to a communication protocol. In this manner,computer-readable media generally may correspond to (1) tangiblecomputer-readable storage media which is non-transitory or (2) acommunication medium such as a signal or carrier wave. Data storagemedia may be any available media that can be accessed by one or morecomputers or one or more processors to retrieve instructions, codeand/or data structures for implementation of the techniques described inthis disclosure. A computer program product may include acomputer-readable medium.

By way of example, and not limitation, such computer-readable storagemedia can comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage, or other magnetic storage devices, flashmemory, or any other medium that can be used to store desired programcode in the form of instructions or data structures and that can beaccessed by a computer. Also, any connection is properly termed acomputer-readable medium. For example, if instructions are transmittedfrom a website, server, or other remote source using a coaxial cable,fiber optic cable, twisted pair, digital subscriber line (DSL), orwireless technologies such as infrared, radio, and microwave, then thecoaxial cable, fiber optic cable, twisted pair, DSL, or wirelesstechnologies such as infrared, radio, and microwave are included in thedefinition of medium. It should be understood, however, thatcomputer-readable storage media and data storage media do not includeconnections, carrier waves, signals, or other transitory media, but areinstead directed to non-transitory, tangible storage media. Disk anddisc, as used herein, includes compact disc (CD), laser disc, opticaldisc, digital versatile disc (DVD), floppy disk and Blu-ray disc, wheredisks usually reproduce data magnetically, while discs reproduce dataoptically with lasers. Combinations of the above should also be includedwithin the scope of computer-readable media.

Instructions may be executed by one or more processors, such as one ormore digital signal processors (DSPs), general purpose microprocessors,application specific integrated circuits (ASICs), field programmablegate arrays (FPGAs), or other equivalent integrated or discrete logiccircuitry. Accordingly, the terms “processor” and “processingcircuitry,” as used herein may refer to any of the foregoing structuresor any other structure suitable for implementation of the techniquesdescribed herein. In addition, in some aspects, the functionalitydescribed herein may be provided within dedicated hardware and/orsoftware modules configured for encoding and decoding, or incorporatedin a combined codec. Also, the techniques could be fully implemented inone or more circuits or logic elements.

The techniques of this disclosure may be implemented in a wide varietyof devices or apparatuses, including a wireless handset, an integratedcircuit (IC) or a set of ICs (e.g., a chip set). Various components,modules, or units are described in this disclosure to emphasizefunctional aspects of devices configured to perform the disclosedtechniques, but do not necessarily require realization by differenthardware units. Rather, as described above, various units may becombined in a codec hardware unit or provided by a collection ofinteroperative hardware units, including one or more processors asdescribed above, in conjunction with suitable software and/or firmware.

Various examples have been described. These and other examples arewithin the scope of the following claims.

What is claimed is:
 1. A method of decoding video data, the methodcomprising: determining an intra-prediction angle for a current block ofvideo data; calculating a displacement value according to theintra-prediction angle; generating an intra-prediction block for thecurrent block of video data using an angular intra-prediction modecorresponding to the intra-prediction angle, the angularintra-prediction mode being an upper-right angular intra-prediction modeor a lower-left angular intra-prediction mode; determining that aposition of a secondary boundary sample of a secondary boundary of theintra-prediction block is a fractional pixel position according toposition-dependent intra-prediction (PDPC) mode and the displacementvalue, such that the secondary boundary sample is not available; inresponse to the secondary boundary sample not being available:interpolating an interpolated value to replace a value of the secondaryboundary sample of the secondary boundary that is not available; for atleast one sample of the intra-prediction block for the current block:calculating a gradient term for the at least one sample using theinterpolated value; and combining a value of an intra-predicted sampleof the intra-prediction block at a position of the at least one sampleof the intra-prediction block with the gradient term to produce a valueof the at least one sample of the intra-prediction block; and decodingthe current block using the intra-prediction block.
 2. The method ofclaim 1, wherein the angular intra-prediction mode comprises theupper-right angular intra-prediction mode having a mode number greaterthan 50 and less than
 81. 3. The method of claim 1, wherein the angularintra-prediction mode comprises the lower-left angular intra-predictionmode having a mode number less than 18 and not being 0 or
 1. 4. Themethod of claim 1, wherein the displacement value has an integercomponent and a fractional component.
 5. The method of claim 4, whereincalculating the displacement value comprises: calculating the integercomponent as being equal to d>>5, wherein >>represents a bitwiseright-shift operator; and calculating the fractional component accordingto d &
 31. 6. The method of claim 5, wherein the integer component ofthe displacement value comprises dInt, wherein the fractional componentof the displacement value comprises dFrac, and wherein interpolating theinterpolated value comprises calculating the interpolated valueaccording to ((32−dFrac)*Q(dInt)+dFrac*Q(dInt+1)+16)>>5.
 7. The methodof claim 6, wherein Q(i) is r(−1+i, −1) when the angularintra-prediction mode is the upper-right angular intra-prediction mode.8. The method of claim 6, wherein Q(i) is r(−1, −1+i) when the angularintra-prediction mode is the lower-left angular intra-prediction mode.9. The method of claim 1, wherein decoding the current block comprises:decoding a residual block for the current block; and combining theintra-prediction block with the residual block to produce a decodedversion of the current block.
 10. The method of claim 1, furthercomprising encoding the current block prior to decoding the currentblock, wherein encoding the current block comprises: calculating aresidual block representing differences between the current block andthe intra-prediction block; and encoding the residual block.
 11. Adevice for decoding video data, the device comprising: a memoryconfigured to store video data; and one or more processors implementedin circuitry and configured to: determine an intra-prediction angle fora current block of video data; calculate a displacement value accordingto the intra-prediction angle; generate an intra-prediction block forthe current block of video data using an angular intra-prediction modecorresponding to the intra-prediction angle, the angularintra-prediction mode being an upper-right angular intra-prediction modeor a lower-left angular intra-prediction mode; determine that a positionof a secondary boundary sample of a secondary boundary of theintra-prediction block is a fractional pixel position according toposition-dependent intra-prediction (PDPC) mode and the displacementvalue, such that the secondary boundary sample is not available; inresponse to the secondary boundary sample not being available:interpolate an interpolated value to replace a value of the secondaryboundary sample of the secondary boundary that is not available; for atleast one sample of the intra-prediction block for the current block:calculate a gradient term for the at least one sample using theinterpolated value; and combine a value of an intra-predicted sample ofthe intra-prediction block at a position of the at least one sample ofthe intra-prediction block with the gradient term to produce a value ofthe at least one sample of the intra-prediction block; and decode thecurrent block using the intra-prediction block.
 12. The device of claim11, wherein the displacement value has an integer component and afractional component.
 13. The device of claim 12, wherein to calculatethe displacement value, the one or more processors are configured to:calculate the integer component as being equal to d>>5,wherein >>represents a bitwise right-shift operator; and calculate thefractional component according to d &
 31. 14. The device of claim 13,wherein the integer component of the displacement value comprises dInt,wherein the fractional component of the displacement value comprisesdFrac, and wherein to interpolate the interpolated value, the one ormore processors are configured to calculate the interpolated valueaccording to ((32−dFrac)*Q(dInt)+dFrac*Q(dInt+1)+16)>>5.
 15. The deviceof claim 14, wherein Q(i) is r(−1+i, −1) when the angularintra-prediction mode is the upper-right angular intra-prediction mode.16. The device of claim 14, wherein Q(i) is r(−1, −1+i) when the angularintra-prediction mode is the lower-left angular intra-prediction mode.17. A computer-readable storage medium having stored thereoninstructions that, when executed, cause a processor to: determine anintra-prediction angle for a current block of video data; calculate adisplacement value according to the intra-prediction angle; generate anintra-prediction block for the current block of video data using anangular intra-prediction mode corresponding to the intra-predictionangle, the angular intra-prediction mode being an upper-right angularintra-prediction mode or a lower-left angular intra-prediction mode;determine that a position of a secondary boundary sample of a secondaryboundary of the intra-prediction block is a fractional pixel positionaccording to position-dependent intra-prediction (PDPC) mode and thedisplacement value, such that the secondary boundary sample is notavailable; in response to the secondary boundary sample not beingavailable: interpolate an interpolated value to replace a value of thesecondary boundary sample of the secondary boundary that is notavailable; for at least one sample of the intra-prediction block for thecurrent block: calculate a gradient term for the at least one sampleusing the interpolated value; and combine a value of an intra-predictedsample of the intra-prediction block at a position of the at least onesample of the intra-prediction block with the gradient term to produce avalue of the at least one sample of the intra-prediction block; anddecode the current block using the intra-prediction block.
 18. Thecomputer-readable storage medium of claim 17, wherein the displacementvalue has an integer component (dInt) and a fractional component(dFrac), wherein the instructions that cause the processor to calculatethe displacement value comprise instructions that cause the processorto: calculate the integer component as being equal to d>>5,wherein >>represents a bitwise right-shift operator; and calculate thefractional component according to d & 31, wherein the instructions thatcause the processor to interpolate the interpolated value compriseinstructions that cause the processor to calculate the interpolatedvalue according to ((32−dFrac)*Q(dInt)+dFrac*Q(dInt+1)+16)>>5, whereinQ(i) is r(−1+i, −1) when the angular intra-prediction mode is theupper-right angular intra-prediction mode, or wherein Q(i) is r(−1,−1+i) when the angular intra-prediction mode is the lower-left angularintra-prediction mode.
 19. A device for decoding video data, the devicecomprising: means for determining an intra-prediction angle for acurrent block of video data; means for calculating a displacement valueaccording to the intra-prediction angle; means for generating anintra-prediction block for the current block of video data using anangular intra-prediction mode corresponding to the intra-predictionangle, the angular intra-prediction mode being an upper-right angularintra-prediction mode or a lower-left angular intra-prediction mode;means for determining that a position of a secondary boundary sample ofa secondary boundary of the intra-prediction block is a fractional pixelposition according to position-dependent intra-prediction (PDPC) modeand the displacement value, such that the secondary boundary sample isnot available; means for interpolating an interpolated value to replacea value of the secondary boundary sample of the secondary boundary thatis not available in response to the secondary boundary sample not beingavailable; means for calculating a gradient term for at least one sampleof the intra-prediction block of the current block using theinterpolated value in response to the secondary boundary sample notbeing available; means for combining a value of an intra-predictedsample of the intra-prediction block at a position of the at least onesample of the intra-prediction block with the gradient term to produce avalue of the at least one sample of the intra-prediction block inresponse to the secondary boundary sample not being available; and meansfor decoding the current block using the intra-prediction block.
 20. Thedevice of claim 19, wherein the displacement value has an integercomponent (dInt) and a fractional component (dFrac), wherein the meansfor calculating the displacement value comprises: means for calculatingthe integer component as being equal to d>>5, wherein >>represents abitwise right-shift operator; and means for calculating the fractionalcomponent according to d & 31, wherein the means for interpolating theinterpolated value comprises means for calculating the interpolatedvalue according to ((32−dFrac)*Q(dInt)+dFrac*Q(dInt+1)+16)>>5, whereinQ(i) is r(−1+i, −1) when the angular intra-prediction mode is theupper-right angular intra-prediction mode, or wherein Q(i) is r(−1,−1+i) when the angular intra-prediction mode is the lower-left angularintra-prediction mode.